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The right filter, first time.

Name: Definitive Water Technologies Johannesburg
Address: Unit 067, Inospace Allandale Exchange, 917 Morkels Close, Halfway House, Midrand, Gauteng, 1685, ZA
Telephone: +27 75 084 5743

CTCape Town+27 21 851 0133 JHBJohannesburg+27 75 084 5743 WhatsApp JHBJohannesburg

Start here: what is the job?

A customer wants better water and you need to fit the right thing without a chemistry degree. Choose the job; the three steps below change to match it, and the animations further down show how each unit works.

Whole-house filtration on municipal water

In one line: 20 then 5 micron sediment, GAC carbon, a bypass and gauges; UV only if the water is stored or doubtful.

Municipal water arrives chlorinated and usually safe, then a pressure event or a tank sends sediment and taste down the line. The standard job is a point-of-entry set at the meter or the tank: a sediment stage, a carbon stage and, where the customer stores water or the supply is doubtful, UV. Fit it coarse to fine, in the flow direction, with a bypass.

What is usually wrong

Match what the customer complains about to what is in the water, and to the stage that fixes it.

What you seeWhat is happeningThe fix

Brown water after an outage; sand in the aerators: Sediment stirred up in the mains by a pressure change, or the bottom of a storage tank. A sediment cartridge at the entry, sized on the flow, catches it.; Sediment cartridge in a housing
Chlorine taste and smell; the customer buys bottled water: The municipal residual. Carbon takes it out; a GAC cartridge for volume at the entry, a carbon block at the kitchen tap.; Activated carbon: GAC or carbon block
White scale on kettles, taps and the geyser element: Hardness. Cartridges do not remove it; a softener does, sized on the hardness and the daily volume.; Water softener with a brine tank
The customer has a JoJo tank as backup and the water goes off: Chlorine fades in a warm tank and bacteria regrow. Filter and UV at the tank outlet, after the booster pump, and keep the tank dark and sealed.; UV steriliser
Housing sump cracked; leaks at the O-ring: Municipal night pressure above 4 bar and water hammer. Housings are rated 6 bar, but most warranties want a pressure-reducing valve ahead of the set above 4 bar.; Pressure-reducing valve ahead of the set
Filters block every few weeks: The stages are in the wrong order or the first one is too fine. Coarse before fine: 20 micron, then 5, then carbon.; Three-stage whole-house set

What to test, and what the numbers mean

A test kit on site and, for a borehole or a rain tank, one laboratory result tell you which stages the job needs. These are the lines to read first for this job, with the numbers that decide the selection.

Read these first for this job
The line on the certificate	What it tells you	Municipal supply	Borehole	Rain tank
Free chlorine	The municipal residual; taste and smell, and it damages RO membranes.	Typically 0.2 to 1 mg/L at the tap. Carbon block or GAC removes it; put carbon ahead of any RO.	None, unless you dose it. If you chlorinate for bacteria, carbon after the contact tank takes the taste out at the kitchen.	None. If the tank is dosed, the same applies.
Hardness	Calcium and magnesium as mg/L CaCO₃; the scale on kettles and elements. A drop-count kit or strip reads it on site.	Cape Town under about 60 mg/L, Rand Water roughly 60 to 110. Above about 120 the customer sees scale and a UV needs softening ahead of it; above about 200 a softener earns its keep (rule of thumb).	Often 200 to 600 in dolomitic and Karoo water. Size the softener on the number and the daily volume, and put it after the iron filter.	Near zero. Rain needs no softener; it needs the opposite, a calcite stage.
Turbidity and sand	Cloudiness and grit. It blocks cartridges, hides germs from UV and scores pump seals.	Spikes after outages. A 20 micron then 5 micron cartridge set handles it.	Sand needs a backwashing vessel; cartridges are for polishing after it. Below 1 NTU before the UV.	Leaves, dust and roof grit: screens and first flush, then a 20 and a 5 micron cartridge.
Flow and pressure	Litres per minute at the point of entry and the bar behind it. Not a lab line, but it sizes every stage.	A house peaks at roughly 20 to 40 L/min. A 10 inch cartridge is a single-tap device; a 20 inch Big Blue set carries a house. Every stage costs pressure, so keep the count honest.	The pump sets the flow. Vessels are sized on linear velocity and need a backwash flow two to three times service; check the pump can deliver it or the media never cleans.	A booster pump after the tank sets the flow; size the cartridges and the UV on the pump's curve, not the tank's outlet.
E. coli and coliforms	Bacteria from sewage, animals and dirty tanks. E. coli means faecal contamination and must be absent; coliforms on their own still mean something is getting in, and the water needs disinfection before anyone drinks it. You cannot see, taste or strip-test them: it is a laboratory line, and it decides whether UV or UF is part of the job.	Should be zero at the tap; the risk is the customer's own storage tank. UV at the tank outlet.	Any E. coli, or coliforms, means UV or chlorine for the whole supply and a look at the wellhead. SANS 241: E. coli zero in 100 mL, total coliforms under 10.	Assume it is there. UV or UF before anyone drinks it.

Read these first for this job

Free chlorine
The municipal residual; taste and smell, and it damages RO membranes.
Municipal supply
Typically 0.2 to 1 mg/L at the tap. Carbon block or GAC removes it; put carbon ahead of any RO.
Borehole
None, unless you dose it. If you chlorinate for bacteria, carbon after the contact tank takes the taste out at the kitchen.
Rain tank
None. If the tank is dosed, the same applies.
Hardness
Calcium and magnesium as mg/L CaCO₃; the scale on kettles and elements. A drop-count kit or strip reads it on site.
Municipal supply
Cape Town under about 60 mg/L, Rand Water roughly 60 to 110. Above about 120 the customer sees scale and a UV needs softening ahead of it; above about 200 a softener earns its keep (rule of thumb).
Borehole
Often 200 to 600 in dolomitic and Karoo water. Size the softener on the number and the daily volume, and put it after the iron filter.
Rain tank
Near zero. Rain needs no softener; it needs the opposite, a calcite stage.
Turbidity and sand
Cloudiness and grit. It blocks cartridges, hides germs from UV and scores pump seals.
Municipal supply
Spikes after outages. A 20 micron then 5 micron cartridge set handles it.
Borehole
Sand needs a backwashing vessel; cartridges are for polishing after it. Below 1 NTU before the UV.
Rain tank
Leaves, dust and roof grit: screens and first flush, then a 20 and a 5 micron cartridge.
Flow and pressure
Litres per minute at the point of entry and the bar behind it. Not a lab line, but it sizes every stage.
Municipal supply
A house peaks at roughly 20 to 40 L/min. A 10 inch cartridge is a single-tap device; a 20 inch Big Blue set carries a house. Every stage costs pressure, so keep the count honest.
Borehole
The pump sets the flow. Vessels are sized on linear velocity and need a backwash flow two to three times service; check the pump can deliver it or the media never cleans.
Rain tank
A booster pump after the tank sets the flow; size the cartridges and the UV on the pump's curve, not the tank's outlet.
E. coli and coliforms
Bacteria from sewage, animals and dirty tanks. E. coli means faecal contamination and must be absent; coliforms on their own still mean something is getting in, and the water needs disinfection before anyone drinks it. You cannot see, taste or strip-test them: it is a laboratory line, and it decides whether UV or UF is part of the job.
Municipal supply
Should be zero at the tap; the risk is the customer's own storage tank. UV at the tank outlet.
Borehole
Any E. coli, or coliforms, means UV or chlorine for the whole supply and a look at the wellhead. SANS 241: E. coli zero in 100 mL, total coliforms under 10.
Rain tank
Assume it is there. UV or UF before anyone drinks it.

Show every line on the checklist

The rest of the checklist
The line on the certificate	What it tells you	Municipal supply	Borehole	Rain tank
Iron and manganese	Orange and black stains. A strip reads iron on site; the certificate gives both.	Rarely above 0.3 mg/L; a rusty pipe or a tank is the usual source.	Above 0.3 mg/L iron or 0.1 manganese (SANS 241) it stains and fouls everything downstream. A catalytic media vessel with aeration or chlorine, ahead of the softener, UV and RO.	None from the rain; rust from a steel roof or tank shows up as iron.
TDS (the salt)	Everything dissolved, in mg/L. A pocket meter reads it in seconds and it is the number that decides whether RO is on the table.	Usually 50 to 300 mg/L; no RO needed for salt, only for taste preference.	Anything up to several thousand. Under 1 200 mg/L (SANS 241) it is drinkable; above a few hundred the customer tastes it, and RO at the kitchen tap is the fix.	Very low, often under 50 mg/L. That is why it is corrosive.
pH	Below about 6.5 the water eats copper and steel; above 8 it drops scale.	Municipal water is corrected to about 7 to 8.5. Leave it alone.	Sandy and coastal boreholes can sit at 5 to 6.5 and pit copper; a calcite vessel ahead of the plumbing fixes it.	Rain is sour, roughly 5.5 to 6.5, with no buffer. Fit a calcite stage where it feeds copper or a geyser.

The rest of the checklist

Iron and manganese
Orange and black stains. A strip reads iron on site; the certificate gives both.
Municipal supply
Rarely above 0.3 mg/L; a rusty pipe or a tank is the usual source.
Borehole
Above 0.3 mg/L iron or 0.1 manganese (SANS 241) it stains and fouls everything downstream. A catalytic media vessel with aeration or chlorine, ahead of the softener, UV and RO.
Rain tank
None from the rain; rust from a steel roof or tank shows up as iron.
TDS (the salt)
Everything dissolved, in mg/L. A pocket meter reads it in seconds and it is the number that decides whether RO is on the table.
Municipal supply
Usually 50 to 300 mg/L; no RO needed for salt, only for taste preference.
Borehole
Anything up to several thousand. Under 1 200 mg/L (SANS 241) it is drinkable; above a few hundred the customer tastes it, and RO at the kitchen tap is the fix.
Rain tank
Very low, often under 50 mg/L. That is why it is corrosive.
pH
Below about 6.5 the water eats copper and steel; above 8 it drops scale.
Municipal supply
Municipal water is corrected to about 7 to 8.5. Leave it alone.
Borehole
Sandy and coastal boreholes can sit at 5 to 6.5 and pit copper; a calcite vessel ahead of the plumbing fixes it.
Rain tank
Rain is sour, roughly 5.5 to 6.5, with no buffer. Fit a calcite stage where it feeds copper or a geyser.

Sources: SANS 241:2025 for drinking-water limits; NSF/ANSI 55 Class A (40 mJ/cm²) for UV; manufacturer data for cartridges, housings, media and resin as recorded in the DWT knowledge base; SANS 10252-1 for drains and backflow. Rules of thumb are marked.

On site, before you quote

1Ask where the water comes from (municipal, borehole, rain tank, or a mix) and what the customer actually hates: taste, stains, scale, smell, sand, or a sick family. That sentence chooses half the stages.
2Test on site with a kit and a meter: hardness, free chlorine, iron, pH and TDS. Ten minutes, and it separates a carbon job from a softener job from an RO job.
3For a borehole or a rain tank that will be drunk, send a sample to a SANAS laboratory for a SANS 241 analysis before you promise drinking water. Bacteria and nitrate cannot be seen or tasted, and the water changes with the seasons, so the customer retests yearly.
4Measure flow and pressure at the point of entry. Filters, vessels and UV are sized in litres per minute, not by the size of the house, and a booster pump changes the answer.

What fixes it

In the order the water goes through them. Every fix links to a plain-language guide and, where it helps, a calculator.

Sediment cartridge in a housing
Sand, grit and brown water; the first stage of every set, and always ahead of carbon, UF, RO and UV.
A spun polypropylene cartridge (20 micron first, 5 micron after it) in a 10 or 20 inch housing; Big Blue (4.5 inch) housings carry a whole house. Water flows from the outside of the cartridge to the core. Housings hang vertically with the arrow in the flow direction, a bypass and a gauge.
Cartridge types compared Micron ratings: nominal versus absolute Listen to the episode
Activated carbon: GAC or carbon block
Chlorine taste and smell, colour, organics; ahead of RO and UF; the drinking-water stage under the counter.
A GAC cartridge is loose granules the water flows through end to end; it carries volume and is the whole-house choice. A carbon block is a solid tube the water passes through from outside to core; finer, slower, and the kitchen-tap choice. Neither removes hardness, salt or germs.
GAC versus carbon block Activated carbon Listen to the episode
Three-stage whole-house set
Municipal water at the point of entry; the standard job for a house or a small business.
Three 20 inch Big Blue housings on a bracket: 20 micron sediment, 5 micron sediment, then GAC (or a carbon block on a lower-flow site). Coarse to fine, arrows in the flow direction, a bypass loop, isolation valves and a pressure gauge on each side, and the cartridges changed on pressure drop, not on the calendar. A pressure-reducing valve ahead of it where the supply exceeds 4 bar; the housings sold here are 1 inch BSP.
Why filters go coarse to fine When to replace a cartridge Listen to the episode
Water softener with a brine tank
Hardness above about 120 to 200 mg/L; geysers, kettles, dishwashers and boilers that scale.
Resin in an FRP vessel with a softener valve and a brine tank of salt. Hard water goes down through the resin, which swaps calcium and magnesium for sodium. When the resin is full the valve backwashes, draws brine through the bed to drain, rinses and refills the brine tank. Metered regeneration, a drain with an air gap, a bypass, and never on the garden tap.
How a water softener works Softener sizing basics Listen to the episode Calculator
UV steriliser
Tank water, borehole water and rainwater that will be drunk; any E. coli or coliforms on a certificate.
A stainless chamber with a lamp in a quartz sleeve; water passes the lamp and the dose kills what is in it. Size it on the flow quoted at 40 mJ/cm² (NSF Class A), not the higher flow quoted at 30 mJ/cm² on the same sheet. It wants clear water: 5 micron ahead of it, iron under 0.3 mg/L, hardness under about 120 mg/L or a softener first, turbidity under 1 NTU. The water around the sleeve also carries the lamp's heat away, so a chamber that holds air or drains cooks the lamp and shortens its life. Mount it vertically with the inlet at the bottom and the outlet at the top, or horizontally with both ports facing up; either way the chamber stays full and air leaves through the outlet. Close to the point of use, room to pull the sleeve, lamp changed yearly whether or not it still glows.
Why a 5 micron prefilter ahead of UV is mandatory UV dose explained Listen to the episode
Pressure-reducing valve ahead of the set
Supply pressure above 4 bar, night pressure spikes, water hammer, cracked sumps and weeping O-rings.
A plumbing fitting, not a treatment stage: a pressure-reducing valve at the point of entry, set to about 3 to 4 bar, with a gauge after it. Housings are rated 6 bar and most warranties want the valve above 4; it also protects the RO and the geyser valve downstream. Any plumbing merchant stocks them.
The commissioning faults we see most

Under-counter drinking water

In one line: a carbon block for taste, UF if germs are the worry, RO only if the water is brak; test the TDS first.

The customer wants water they are happy to drink from one tap. Three families answer that: a carbon block for taste and chlorine on municipal water, an ultrafiltration cartridge when germs are the worry, and reverse osmosis when the water is brak or the customer wants the salts out. Each is a different unit with a different install, and only one of them needs a drain.

What is usually wrong

Match what the customer complains about to what is in the water, and to the stage that fixes it.

What you seeWhat is happeningThe fix

Tastes and smells of chlorine: Municipal residual. A carbon block under the counter with its own tap is the standard job.; Activated carbon: GAC or carbon block
Family gets stomach upsets; the water is from a tank or a borehole: Bacteria. An ultrafiltration cartridge physically removes them without a drain or power; UV does the same for the whole house.; Ultrafiltration cartridge
Water tastes salty or brak; white film on the kettle: Dissolved salts and hardness. Only reverse osmosis takes salt out; it needs a drain connection and a storage tank, and it is the right answer for TDS above a few hundred mg/L.; Under-counter reverse osmosis
The RO you fitted last year drips slowly and the customer complains: Blocked pre-filters or a fouled membrane; RO on hard or dirty water needs its sediment and carbon stages changed on time, and a softener ahead of it where the water is hard.; Under-counter reverse osmosis

What to test, and what the numbers mean

Read these first for this job
The line on the certificate	What it tells you	Municipal supply	Borehole	Rain tank
Free chlorine	The municipal residual; taste and smell, and it damages RO membranes.	Typically 0.2 to 1 mg/L at the tap. Carbon block or GAC removes it; put carbon ahead of any RO.	None, unless you dose it. If you chlorinate for bacteria, carbon after the contact tank takes the taste out at the kitchen.	None. If the tank is dosed, the same applies.
TDS (the salt)	Everything dissolved, in mg/L. A pocket meter reads it in seconds and it is the number that decides whether RO is on the table.	Usually 50 to 300 mg/L; no RO needed for salt, only for taste preference.	Anything up to several thousand. Under 1 200 mg/L (SANS 241) it is drinkable; above a few hundred the customer tastes it, and RO at the kitchen tap is the fix.	Very low, often under 50 mg/L. That is why it is corrosive.
E. coli and coliforms	Bacteria from sewage, animals and dirty tanks. E. coli means faecal contamination and must be absent; coliforms on their own still mean something is getting in, and the water needs disinfection before anyone drinks it. You cannot see, taste or strip-test them: it is a laboratory line, and it decides whether UV or UF is part of the job.	Should be zero at the tap; the risk is the customer's own storage tank. UV at the tank outlet.	Any E. coli, or coliforms, means UV or chlorine for the whole supply and a look at the wellhead. SANS 241: E. coli zero in 100 mL, total coliforms under 10.	Assume it is there. UV or UF before anyone drinks it.
Hardness	Calcium and magnesium as mg/L CaCO₃; the scale on kettles and elements. A drop-count kit or strip reads it on site.	Cape Town under about 60 mg/L, Rand Water roughly 60 to 110. Above about 120 the customer sees scale and a UV needs softening ahead of it; above about 200 a softener earns its keep (rule of thumb).	Often 200 to 600 in dolomitic and Karoo water. Size the softener on the number and the daily volume, and put it after the iron filter.	Near zero. Rain needs no softener; it needs the opposite, a calcite stage.

Read these first for this job

Free chlorine
The municipal residual; taste and smell, and it damages RO membranes.
Municipal supply
Typically 0.2 to 1 mg/L at the tap. Carbon block or GAC removes it; put carbon ahead of any RO.
Borehole
None, unless you dose it. If you chlorinate for bacteria, carbon after the contact tank takes the taste out at the kitchen.
Rain tank
None. If the tank is dosed, the same applies.
TDS (the salt)
Everything dissolved, in mg/L. A pocket meter reads it in seconds and it is the number that decides whether RO is on the table.
Municipal supply
Usually 50 to 300 mg/L; no RO needed for salt, only for taste preference.
Borehole
Anything up to several thousand. Under 1 200 mg/L (SANS 241) it is drinkable; above a few hundred the customer tastes it, and RO at the kitchen tap is the fix.
Rain tank
Very low, often under 50 mg/L. That is why it is corrosive.
E. coli and coliforms
Bacteria from sewage, animals and dirty tanks. E. coli means faecal contamination and must be absent; coliforms on their own still mean something is getting in, and the water needs disinfection before anyone drinks it. You cannot see, taste or strip-test them: it is a laboratory line, and it decides whether UV or UF is part of the job.
Municipal supply
Should be zero at the tap; the risk is the customer's own storage tank. UV at the tank outlet.
Borehole
Any E. coli, or coliforms, means UV or chlorine for the whole supply and a look at the wellhead. SANS 241: E. coli zero in 100 mL, total coliforms under 10.
Rain tank
Assume it is there. UV or UF before anyone drinks it.
Hardness
Calcium and magnesium as mg/L CaCO₃; the scale on kettles and elements. A drop-count kit or strip reads it on site.
Municipal supply
Cape Town under about 60 mg/L, Rand Water roughly 60 to 110. Above about 120 the customer sees scale and a UV needs softening ahead of it; above about 200 a softener earns its keep (rule of thumb).
Borehole
Often 200 to 600 in dolomitic and Karoo water. Size the softener on the number and the daily volume, and put it after the iron filter.
Rain tank
Near zero. Rain needs no softener; it needs the opposite, a calcite stage.

Show every line on the checklist

The rest of the checklist
The line on the certificate	What it tells you	Municipal supply	Borehole	Rain tank
Iron and manganese	Orange and black stains. A strip reads iron on site; the certificate gives both.	Rarely above 0.3 mg/L; a rusty pipe or a tank is the usual source.	Above 0.3 mg/L iron or 0.1 manganese (SANS 241) it stains and fouls everything downstream. A catalytic media vessel with aeration or chlorine, ahead of the softener, UV and RO.	None from the rain; rust from a steel roof or tank shows up as iron.
pH	Below about 6.5 the water eats copper and steel; above 8 it drops scale.	Municipal water is corrected to about 7 to 8.5. Leave it alone.	Sandy and coastal boreholes can sit at 5 to 6.5 and pit copper; a calcite vessel ahead of the plumbing fixes it.	Rain is sour, roughly 5.5 to 6.5, with no buffer. Fit a calcite stage where it feeds copper or a geyser.
Turbidity and sand	Cloudiness and grit. It blocks cartridges, hides germs from UV and scores pump seals.	Spikes after outages. A 20 micron then 5 micron cartridge set handles it.	Sand needs a backwashing vessel; cartridges are for polishing after it. Below 1 NTU before the UV.	Leaves, dust and roof grit: screens and first flush, then a 20 and a 5 micron cartridge.
Flow and pressure	Litres per minute at the point of entry and the bar behind it. Not a lab line, but it sizes every stage.	A house peaks at roughly 20 to 40 L/min. A 10 inch cartridge is a single-tap device; a 20 inch Big Blue set carries a house. Every stage costs pressure, so keep the count honest.	The pump sets the flow. Vessels are sized on linear velocity and need a backwash flow two to three times service; check the pump can deliver it or the media never cleans.	A booster pump after the tank sets the flow; size the cartridges and the UV on the pump's curve, not the tank's outlet.

The rest of the checklist

Iron and manganese
Orange and black stains. A strip reads iron on site; the certificate gives both.
Municipal supply
Rarely above 0.3 mg/L; a rusty pipe or a tank is the usual source.
Borehole
Above 0.3 mg/L iron or 0.1 manganese (SANS 241) it stains and fouls everything downstream. A catalytic media vessel with aeration or chlorine, ahead of the softener, UV and RO.
Rain tank
None from the rain; rust from a steel roof or tank shows up as iron.
pH
Below about 6.5 the water eats copper and steel; above 8 it drops scale.
Municipal supply
Municipal water is corrected to about 7 to 8.5. Leave it alone.
Borehole
Sandy and coastal boreholes can sit at 5 to 6.5 and pit copper; a calcite vessel ahead of the plumbing fixes it.
Rain tank
Rain is sour, roughly 5.5 to 6.5, with no buffer. Fit a calcite stage where it feeds copper or a geyser.
Turbidity and sand
Cloudiness and grit. It blocks cartridges, hides germs from UV and scores pump seals.
Municipal supply
Spikes after outages. A 20 micron then 5 micron cartridge set handles it.
Borehole
Sand needs a backwashing vessel; cartridges are for polishing after it. Below 1 NTU before the UV.
Rain tank
Leaves, dust and roof grit: screens and first flush, then a 20 and a 5 micron cartridge.
Flow and pressure
Litres per minute at the point of entry and the bar behind it. Not a lab line, but it sizes every stage.
Municipal supply
A house peaks at roughly 20 to 40 L/min. A 10 inch cartridge is a single-tap device; a 20 inch Big Blue set carries a house. Every stage costs pressure, so keep the count honest.
Borehole
The pump sets the flow. Vessels are sized on linear velocity and need a backwash flow two to three times service; check the pump can deliver it or the media never cleans.
Rain tank
A booster pump after the tank sets the flow; size the cartridges and the UV on the pump's curve, not the tank's outlet.

On site, before you quote

1Ask where the water comes from (municipal, borehole, rain tank, or a mix) and what the customer actually hates: taste, stains, scale, smell, sand, or a sick family. That sentence chooses half the stages.
2Test on site with a kit and a meter: hardness, free chlorine, iron, pH and TDS. Ten minutes, and it separates a carbon job from a softener job from an RO job.
3For a borehole or a rain tank that will be drunk, send a sample to a SANAS laboratory for a SANS 241 analysis before you promise drinking water. Bacteria and nitrate cannot be seen or tasted, and the water changes with the seasons, so the customer retests yearly.
4Measure flow and pressure at the point of entry. Filters, vessels and UV are sized in litres per minute, not by the size of the house, and a booster pump changes the answer.

What fixes it

In the order the water goes through them. Every fix links to a plain-language guide and, where it helps, a calculator.

Activated carbon: GAC or carbon block
Chlorine taste and smell, colour, organics; ahead of RO and UF; the drinking-water stage under the counter.
A GAC cartridge is loose granules the water flows through end to end; it carries volume and is the whole-house choice. A carbon block is a solid tube the water passes through from outside to core; finer, slower, and the kitchen-tap choice. Neither removes hardness, salt or germs.
GAC versus carbon block Activated carbon Listen to the episode
Ultrafiltration cartridge
Bacteria and cysts at a single tap, without power or a drain; tank and borehole water for one kitchen.
Hollow-fibre membranes with pores far smaller than a bacterium. Water passes through the fibre wall; germs and turbidity stay behind. It keeps the minerals, needs a sediment stage ahead of it, and is flushed rather than backwashed.
What UV does and does not do Cartridge types compared Listen to the episode
Under-counter reverse osmosis
Brak or salty water, high TDS, or a customer who wants the salts and everything else out at the kitchen tap.
Sediment and carbon pre-filters, a membrane, a pressurised storage tank, a drain saddle for the reject water and its own tap. It needs a drain and at least about 3 bar, or a booster pump. A softener or antiscalant ahead of it where the water is hard, and a remineralising cartridge after it if the customer wants the taste back.
How reverse osmosis works Permeate quality Listen to the episode Calculator

Basic borehole filtration

In one line: laboratory test first, then a backwashing vessel for sand, an iron vessel if it stains, a softener if it scales, UV before anyone drinks it.

A borehole is untreated groundwater, so the job starts with a laboratory result, not a catalogue. Four things cover most of it: a backwashing sand or glass vessel for sand, a catalytic vessel with aeration or chlorine for iron and manganese, a softener for hardness, and UV or chlorine for germs, in that order. Cartridges alone on a borehole are a callback waiting to happen.

What is usually wrong

Match what the customer complains about to what is in the water, and to the stage that fixes it.

What you seeWhat is happeningThe fix

Sand and grit; cartridges block in days: Fine sand from the aquifer. A backwashing FRP vessel with sand or glass media carries it; a cartridge does not.; FRP vessel with a backwashing valve
Orange stains, rusty tank water, black slime: Dissolved iron and manganese. Oxidise with air or chlorine, then a catalytic media vessel that backwashes at the rate the media asks for.; Iron and manganese vessel
Rotten-egg smell: Hydrogen sulphide. Aeration or a small chlorine dose oxidises it, and the same catalytic bed takes the rest.; Iron and manganese vessel
Scale everywhere; the geyser element dies: Hardness, often heavy in dolomitic and Karoo water. A softener sized on the hardness and the daily volume, with a metered valve.; Water softener with a brine tank
E. coli or coliforms on the certificate: Surface contamination reaching the borehole. UV after a 5 micron cartridge, or chlorine dosing into a contact tank; and fix the wellhead seal.; UV steriliser
Water tastes salty: Brak groundwater. Reverse osmosis at the kitchen tap for drinking; the rest of the house lives with it or blends.; Under-counter reverse osmosis

What to test, and what the numbers mean

Read these first for this job
The line on the certificate	What it tells you	Municipal supply	Borehole	Rain tank
Turbidity and sand	Cloudiness and grit. It blocks cartridges, hides germs from UV and scores pump seals.	Spikes after outages. A 20 micron then 5 micron cartridge set handles it.	Sand needs a backwashing vessel; cartridges are for polishing after it. Below 1 NTU before the UV.	Leaves, dust and roof grit: screens and first flush, then a 20 and a 5 micron cartridge.
Iron and manganese	Orange and black stains. A strip reads iron on site; the certificate gives both.	Rarely above 0.3 mg/L; a rusty pipe or a tank is the usual source.	Above 0.3 mg/L iron or 0.1 manganese (SANS 241) it stains and fouls everything downstream. A catalytic media vessel with aeration or chlorine, ahead of the softener, UV and RO.	None from the rain; rust from a steel roof or tank shows up as iron.
Hardness	Calcium and magnesium as mg/L CaCO₃; the scale on kettles and elements. A drop-count kit or strip reads it on site.	Cape Town under about 60 mg/L, Rand Water roughly 60 to 110. Above about 120 the customer sees scale and a UV needs softening ahead of it; above about 200 a softener earns its keep (rule of thumb).	Often 200 to 600 in dolomitic and Karoo water. Size the softener on the number and the daily volume, and put it after the iron filter.	Near zero. Rain needs no softener; it needs the opposite, a calcite stage.
E. coli and coliforms	Bacteria from sewage, animals and dirty tanks. E. coli means faecal contamination and must be absent; coliforms on their own still mean something is getting in, and the water needs disinfection before anyone drinks it. You cannot see, taste or strip-test them: it is a laboratory line, and it decides whether UV or UF is part of the job.	Should be zero at the tap; the risk is the customer's own storage tank. UV at the tank outlet.	Any E. coli, or coliforms, means UV or chlorine for the whole supply and a look at the wellhead. SANS 241: E. coli zero in 100 mL, total coliforms under 10.	Assume it is there. UV or UF before anyone drinks it.
TDS (the salt)	Everything dissolved, in mg/L. A pocket meter reads it in seconds and it is the number that decides whether RO is on the table.	Usually 50 to 300 mg/L; no RO needed for salt, only for taste preference.	Anything up to several thousand. Under 1 200 mg/L (SANS 241) it is drinkable; above a few hundred the customer tastes it, and RO at the kitchen tap is the fix.	Very low, often under 50 mg/L. That is why it is corrosive.
pH	Below about 6.5 the water eats copper and steel; above 8 it drops scale.	Municipal water is corrected to about 7 to 8.5. Leave it alone.	Sandy and coastal boreholes can sit at 5 to 6.5 and pit copper; a calcite vessel ahead of the plumbing fixes it.	Rain is sour, roughly 5.5 to 6.5, with no buffer. Fit a calcite stage where it feeds copper or a geyser.
Flow and pressure	Litres per minute at the point of entry and the bar behind it. Not a lab line, but it sizes every stage.	A house peaks at roughly 20 to 40 L/min. A 10 inch cartridge is a single-tap device; a 20 inch Big Blue set carries a house. Every stage costs pressure, so keep the count honest.	The pump sets the flow. Vessels are sized on linear velocity and need a backwash flow two to three times service; check the pump can deliver it or the media never cleans.	A booster pump after the tank sets the flow; size the cartridges and the UV on the pump's curve, not the tank's outlet.

Read these first for this job

Turbidity and sand
Cloudiness and grit. It blocks cartridges, hides germs from UV and scores pump seals.
Municipal supply
Spikes after outages. A 20 micron then 5 micron cartridge set handles it.
Borehole
Sand needs a backwashing vessel; cartridges are for polishing after it. Below 1 NTU before the UV.
Rain tank
Leaves, dust and roof grit: screens and first flush, then a 20 and a 5 micron cartridge.
Iron and manganese
Orange and black stains. A strip reads iron on site; the certificate gives both.
Municipal supply
Rarely above 0.3 mg/L; a rusty pipe or a tank is the usual source.
Borehole
Above 0.3 mg/L iron or 0.1 manganese (SANS 241) it stains and fouls everything downstream. A catalytic media vessel with aeration or chlorine, ahead of the softener, UV and RO.
Rain tank
None from the rain; rust from a steel roof or tank shows up as iron.
Hardness
Calcium and magnesium as mg/L CaCO₃; the scale on kettles and elements. A drop-count kit or strip reads it on site.
Municipal supply
Cape Town under about 60 mg/L, Rand Water roughly 60 to 110. Above about 120 the customer sees scale and a UV needs softening ahead of it; above about 200 a softener earns its keep (rule of thumb).
Borehole
Often 200 to 600 in dolomitic and Karoo water. Size the softener on the number and the daily volume, and put it after the iron filter.
Rain tank
Near zero. Rain needs no softener; it needs the opposite, a calcite stage.
E. coli and coliforms
Bacteria from sewage, animals and dirty tanks. E. coli means faecal contamination and must be absent; coliforms on their own still mean something is getting in, and the water needs disinfection before anyone drinks it. You cannot see, taste or strip-test them: it is a laboratory line, and it decides whether UV or UF is part of the job.
Municipal supply
Should be zero at the tap; the risk is the customer's own storage tank. UV at the tank outlet.
Borehole
Any E. coli, or coliforms, means UV or chlorine for the whole supply and a look at the wellhead. SANS 241: E. coli zero in 100 mL, total coliforms under 10.
Rain tank
Assume it is there. UV or UF before anyone drinks it.
TDS (the salt)
Everything dissolved, in mg/L. A pocket meter reads it in seconds and it is the number that decides whether RO is on the table.
Municipal supply
Usually 50 to 300 mg/L; no RO needed for salt, only for taste preference.
Borehole
Anything up to several thousand. Under 1 200 mg/L (SANS 241) it is drinkable; above a few hundred the customer tastes it, and RO at the kitchen tap is the fix.
Rain tank
Very low, often under 50 mg/L. That is why it is corrosive.
pH
Below about 6.5 the water eats copper and steel; above 8 it drops scale.
Municipal supply
Municipal water is corrected to about 7 to 8.5. Leave it alone.
Borehole
Sandy and coastal boreholes can sit at 5 to 6.5 and pit copper; a calcite vessel ahead of the plumbing fixes it.
Rain tank
Rain is sour, roughly 5.5 to 6.5, with no buffer. Fit a calcite stage where it feeds copper or a geyser.
Flow and pressure
Litres per minute at the point of entry and the bar behind it. Not a lab line, but it sizes every stage.
Municipal supply
A house peaks at roughly 20 to 40 L/min. A 10 inch cartridge is a single-tap device; a 20 inch Big Blue set carries a house. Every stage costs pressure, so keep the count honest.
Borehole
The pump sets the flow. Vessels are sized on linear velocity and need a backwash flow two to three times service; check the pump can deliver it or the media never cleans.
Rain tank
A booster pump after the tank sets the flow; size the cartridges and the UV on the pump's curve, not the tank's outlet.

Show every line on the checklist

The rest of the checklist
The line on the certificate	What it tells you	Municipal supply	Borehole	Rain tank
Free chlorine	The municipal residual; taste and smell, and it damages RO membranes.	Typically 0.2 to 1 mg/L at the tap. Carbon block or GAC removes it; put carbon ahead of any RO.	None, unless you dose it. If you chlorinate for bacteria, carbon after the contact tank takes the taste out at the kitchen.	None. If the tank is dosed, the same applies.

The rest of the checklist

Free chlorine
The municipal residual; taste and smell, and it damages RO membranes.
Municipal supply
Typically 0.2 to 1 mg/L at the tap. Carbon block or GAC removes it; put carbon ahead of any RO.
Borehole
None, unless you dose it. If you chlorinate for bacteria, carbon after the contact tank takes the taste out at the kitchen.
Rain tank
None. If the tank is dosed, the same applies.

On site, before you quote

1Ask where the water comes from (municipal, borehole, rain tank, or a mix) and what the customer actually hates: taste, stains, scale, smell, sand, or a sick family. That sentence chooses half the stages.
2Test on site with a kit and a meter: hardness, free chlorine, iron, pH and TDS. Ten minutes, and it separates a carbon job from a softener job from an RO job.
3For a borehole or a rain tank that will be drunk, send a sample to a SANAS laboratory for a SANS 241 analysis before you promise drinking water. Bacteria and nitrate cannot be seen or tasted, and the water changes with the seasons, so the customer retests yearly.
4Measure flow and pressure at the point of entry. Filters, vessels and UV are sized in litres per minute, not by the size of the house, and a booster pump changes the answer.

What fixes it

In the order the water goes through them. Every fix links to a plain-language guide and, where it helps, a calculator.

FRP vessel with a backwashing valve
Sand and turbidity on a borehole or dam supply, or any flow a cartridge cannot carry.
A fibreglass vessel (10 x 54, 13 x 54 and up) with a gravel base, a bed of sand or glass media, a riser tube to the bottom strainer and a multiport valve on top. In service the water goes down through the bed and up the riser; on backwash the valve reverses it and sends the dirt to drain; a fast rinse packs the bed again. The valve needs a drain that can take the backwash flow.
How a media filter works Backwashing explained Listen to the episode Calculator
Iron and manganese vessel
Orange or black stains, rusty tank water, rotten-egg smell on a borehole.
Oxidise first, with an air injector or a small chlorine dose, then a catalytic media bed in an FRP vessel with a filter valve. The media decides which oxidant: some want air and are ruined by chlorine, others want chlorine, so read the media sheet or ask the branch. The bed asks for a high backwash rate, so the pump must deliver it. It sits before the softener, the UV and any RO.
Catalytic media for iron and manganese Backwashing explained Listen to the episode Calculator
Water softener with a brine tank
Hardness above about 120 to 200 mg/L; geysers, kettles, dishwashers and boilers that scale.
Resin in an FRP vessel with a softener valve and a brine tank of salt. Hard water goes down through the resin, which swaps calcium and magnesium for sodium. When the resin is full the valve backwashes, draws brine through the bed to drain, rinses and refills the brine tank. Metered regeneration, a drain with an air gap, a bypass, and never on the garden tap.
How a water softener works Softener sizing basics Listen to the episode Calculator
UV steriliser
Tank water, borehole water and rainwater that will be drunk; any E. coli or coliforms on a certificate.
A stainless chamber with a lamp in a quartz sleeve; water passes the lamp and the dose kills what is in it. Size it on the flow quoted at 40 mJ/cm² (NSF Class A), not the higher flow quoted at 30 mJ/cm² on the same sheet. It wants clear water: 5 micron ahead of it, iron under 0.3 mg/L, hardness under about 120 mg/L or a softener first, turbidity under 1 NTU. The water around the sleeve also carries the lamp's heat away, so a chamber that holds air or drains cooks the lamp and shortens its life. Mount it vertically with the inlet at the bottom and the outlet at the top, or horizontally with both ports facing up; either way the chamber stays full and air leaves through the outlet. Close to the point of use, room to pull the sleeve, lamp changed yearly whether or not it still glows.
Why a 5 micron prefilter ahead of UV is mandatory UV dose explained Listen to the episode
Under-counter reverse osmosis
Brak or salty water, high TDS, or a customer who wants the salts and everything else out at the kitchen tap.
Sediment and carbon pre-filters, a membrane, a pressurised storage tank, a drain saddle for the reject water and its own tap. It needs a drain and at least about 3 bar, or a booster pump. A softener or antiscalant ahead of it where the water is hard, and a remineralising cartridge after it if the customer wants the taste back.
How reverse osmosis works Permeate quality Listen to the episode Calculator

Rainwater tank filtration

In one line: screens and a first-flush diverter at the roof, a dark sealed tank, then sediment, carbon and UV at the tap.

Rain off a roof is soft and salt-free; what it carries is whatever was on the roof and in the gutters. The job is to keep the roof out of the tank (gutter screens and a first-flush diverter), keep light out of the tank, and treat what comes out: a sediment cartridge, carbon for taste, and UV if anyone will drink it. Sour rainwater also eats copper, so a calcite stage protects the plumbing.

What is usually wrong

Match what the customer complains about to what is in the water, and to the stage that fixes it.

What you seeWhat is happeningThe fix

Leaves and grit in the tank; cartridges block: No gutter screens and no first-flush diverter. Fit both; then a sediment cartridge lasts.; Roof and tank kit: screens and first flush
Green water: Light in the tank. An opaque tank, a lid, and carbon for the taste.; Activated carbon: GAC or carbon block
The family drinks it and someone gets sick: Bird droppings and leaf litter carry bacteria. UV after a 5 micron cartridge, and a laboratory test once.; UV steriliser
Green stains and pinholes in copper pipes: Rainwater has no lime to buffer it, so its pH sits low. A calcite cartridge or vessel brings it up.; Calcite for sour water

What to test, and what the numbers mean

Read these first for this job
The line on the certificate	What it tells you	Municipal supply	Borehole	Rain tank
E. coli and coliforms	Bacteria from sewage, animals and dirty tanks. E. coli means faecal contamination and must be absent; coliforms on their own still mean something is getting in, and the water needs disinfection before anyone drinks it. You cannot see, taste or strip-test them: it is a laboratory line, and it decides whether UV or UF is part of the job.	Should be zero at the tap; the risk is the customer's own storage tank. UV at the tank outlet.	Any E. coli, or coliforms, means UV or chlorine for the whole supply and a look at the wellhead. SANS 241: E. coli zero in 100 mL, total coliforms under 10.	Assume it is there. UV or UF before anyone drinks it.
pH	Below about 6.5 the water eats copper and steel; above 8 it drops scale.	Municipal water is corrected to about 7 to 8.5. Leave it alone.	Sandy and coastal boreholes can sit at 5 to 6.5 and pit copper; a calcite vessel ahead of the plumbing fixes it.	Rain is sour, roughly 5.5 to 6.5, with no buffer. Fit a calcite stage where it feeds copper or a geyser.
Turbidity and sand	Cloudiness and grit. It blocks cartridges, hides germs from UV and scores pump seals.	Spikes after outages. A 20 micron then 5 micron cartridge set handles it.	Sand needs a backwashing vessel; cartridges are for polishing after it. Below 1 NTU before the UV.	Leaves, dust and roof grit: screens and first flush, then a 20 and a 5 micron cartridge.
Flow and pressure	Litres per minute at the point of entry and the bar behind it. Not a lab line, but it sizes every stage.	A house peaks at roughly 20 to 40 L/min. A 10 inch cartridge is a single-tap device; a 20 inch Big Blue set carries a house. Every stage costs pressure, so keep the count honest.	The pump sets the flow. Vessels are sized on linear velocity and need a backwash flow two to three times service; check the pump can deliver it or the media never cleans.	A booster pump after the tank sets the flow; size the cartridges and the UV on the pump's curve, not the tank's outlet.

Read these first for this job

E. coli and coliforms
Bacteria from sewage, animals and dirty tanks. E. coli means faecal contamination and must be absent; coliforms on their own still mean something is getting in, and the water needs disinfection before anyone drinks it. You cannot see, taste or strip-test them: it is a laboratory line, and it decides whether UV or UF is part of the job.
Municipal supply
Should be zero at the tap; the risk is the customer's own storage tank. UV at the tank outlet.
Borehole
Any E. coli, or coliforms, means UV or chlorine for the whole supply and a look at the wellhead. SANS 241: E. coli zero in 100 mL, total coliforms under 10.
Rain tank
Assume it is there. UV or UF before anyone drinks it.
pH
Below about 6.5 the water eats copper and steel; above 8 it drops scale.
Municipal supply
Municipal water is corrected to about 7 to 8.5. Leave it alone.
Borehole
Sandy and coastal boreholes can sit at 5 to 6.5 and pit copper; a calcite vessel ahead of the plumbing fixes it.
Rain tank
Rain is sour, roughly 5.5 to 6.5, with no buffer. Fit a calcite stage where it feeds copper or a geyser.
Turbidity and sand
Cloudiness and grit. It blocks cartridges, hides germs from UV and scores pump seals.
Municipal supply
Spikes after outages. A 20 micron then 5 micron cartridge set handles it.
Borehole
Sand needs a backwashing vessel; cartridges are for polishing after it. Below 1 NTU before the UV.
Rain tank
Leaves, dust and roof grit: screens and first flush, then a 20 and a 5 micron cartridge.
Flow and pressure
Litres per minute at the point of entry and the bar behind it. Not a lab line, but it sizes every stage.
Municipal supply
A house peaks at roughly 20 to 40 L/min. A 10 inch cartridge is a single-tap device; a 20 inch Big Blue set carries a house. Every stage costs pressure, so keep the count honest.
Borehole
The pump sets the flow. Vessels are sized on linear velocity and need a backwash flow two to three times service; check the pump can deliver it or the media never cleans.
Rain tank
A booster pump after the tank sets the flow; size the cartridges and the UV on the pump's curve, not the tank's outlet.

Show every line on the checklist

The rest of the checklist
The line on the certificate	What it tells you	Municipal supply	Borehole	Rain tank
Hardness	Calcium and magnesium as mg/L CaCO₃; the scale on kettles and elements. A drop-count kit or strip reads it on site.	Cape Town under about 60 mg/L, Rand Water roughly 60 to 110. Above about 120 the customer sees scale and a UV needs softening ahead of it; above about 200 a softener earns its keep (rule of thumb).	Often 200 to 600 in dolomitic and Karoo water. Size the softener on the number and the daily volume, and put it after the iron filter.	Near zero. Rain needs no softener; it needs the opposite, a calcite stage.
Free chlorine	The municipal residual; taste and smell, and it damages RO membranes.	Typically 0.2 to 1 mg/L at the tap. Carbon block or GAC removes it; put carbon ahead of any RO.	None, unless you dose it. If you chlorinate for bacteria, carbon after the contact tank takes the taste out at the kitchen.	None. If the tank is dosed, the same applies.
Iron and manganese	Orange and black stains. A strip reads iron on site; the certificate gives both.	Rarely above 0.3 mg/L; a rusty pipe or a tank is the usual source.	Above 0.3 mg/L iron or 0.1 manganese (SANS 241) it stains and fouls everything downstream. A catalytic media vessel with aeration or chlorine, ahead of the softener, UV and RO.	None from the rain; rust from a steel roof or tank shows up as iron.
TDS (the salt)	Everything dissolved, in mg/L. A pocket meter reads it in seconds and it is the number that decides whether RO is on the table.	Usually 50 to 300 mg/L; no RO needed for salt, only for taste preference.	Anything up to several thousand. Under 1 200 mg/L (SANS 241) it is drinkable; above a few hundred the customer tastes it, and RO at the kitchen tap is the fix.	Very low, often under 50 mg/L. That is why it is corrosive.

The rest of the checklist

Hardness
Calcium and magnesium as mg/L CaCO₃; the scale on kettles and elements. A drop-count kit or strip reads it on site.
Municipal supply
Cape Town under about 60 mg/L, Rand Water roughly 60 to 110. Above about 120 the customer sees scale and a UV needs softening ahead of it; above about 200 a softener earns its keep (rule of thumb).
Borehole
Often 200 to 600 in dolomitic and Karoo water. Size the softener on the number and the daily volume, and put it after the iron filter.
Rain tank
Near zero. Rain needs no softener; it needs the opposite, a calcite stage.
Free chlorine
The municipal residual; taste and smell, and it damages RO membranes.
Municipal supply
Typically 0.2 to 1 mg/L at the tap. Carbon block or GAC removes it; put carbon ahead of any RO.
Borehole
None, unless you dose it. If you chlorinate for bacteria, carbon after the contact tank takes the taste out at the kitchen.
Rain tank
None. If the tank is dosed, the same applies.
Iron and manganese
Orange and black stains. A strip reads iron on site; the certificate gives both.
Municipal supply
Rarely above 0.3 mg/L; a rusty pipe or a tank is the usual source.
Borehole
Above 0.3 mg/L iron or 0.1 manganese (SANS 241) it stains and fouls everything downstream. A catalytic media vessel with aeration or chlorine, ahead of the softener, UV and RO.
Rain tank
None from the rain; rust from a steel roof or tank shows up as iron.
TDS (the salt)
Everything dissolved, in mg/L. A pocket meter reads it in seconds and it is the number that decides whether RO is on the table.
Municipal supply
Usually 50 to 300 mg/L; no RO needed for salt, only for taste preference.
Borehole
Anything up to several thousand. Under 1 200 mg/L (SANS 241) it is drinkable; above a few hundred the customer tastes it, and RO at the kitchen tap is the fix.
Rain tank
Very low, often under 50 mg/L. That is why it is corrosive.

On site, before you quote

1Ask where the water comes from (municipal, borehole, rain tank, or a mix) and what the customer actually hates: taste, stains, scale, smell, sand, or a sick family. That sentence chooses half the stages.
2Test on site with a kit and a meter: hardness, free chlorine, iron, pH and TDS. Ten minutes, and it separates a carbon job from a softener job from an RO job.
3For a borehole or a rain tank that will be drunk, send a sample to a SANAS laboratory for a SANS 241 analysis before you promise drinking water. Bacteria and nitrate cannot be seen or tasted, and the water changes with the seasons, so the customer retests yearly.
4Measure flow and pressure at the point of entry. Filters, vessels and UV are sized in litres per minute, not by the size of the house, and a booster pump changes the answer.

What fixes it

In the order the water goes through them. Every fix links to a plain-language guide and, where it helps, a calculator.

Roof and tank kit: screens and first flush
Every rain tank, before any filter.
Gutter screens keep the leaves out; a first-flush diverter discards the first dirty litres of every storm; a tank screen on the inlet keeps mosquitoes and frogs out; an opaque, covered tank keeps the light out. Then the filters have a chance.
Backup water: tanks, boreholes and rain Drought-proofing the farm supply Listen to the episode
Sediment cartridge in a housing
Sand, grit and brown water; the first stage of every set, and always ahead of carbon, UF, RO and UV.
A spun polypropylene cartridge (20 micron first, 5 micron after it) in a 10 or 20 inch housing; Big Blue (4.5 inch) housings carry a whole house. Water flows from the outside of the cartridge to the core. Housings hang vertically with the arrow in the flow direction, a bypass and a gauge.
Cartridge types compared Micron ratings: nominal versus absolute Listen to the episode
Activated carbon: GAC or carbon block
Chlorine taste and smell, colour, organics; ahead of RO and UF; the drinking-water stage under the counter.
A GAC cartridge is loose granules the water flows through end to end; it carries volume and is the whole-house choice. A carbon block is a solid tube the water passes through from outside to core; finer, slower, and the kitchen-tap choice. Neither removes hardness, salt or germs.
GAC versus carbon block Activated carbon Listen to the episode
Calcite for sour water
Rainwater and low-pH boreholes that eat copper and steel.
A cartridge or vessel of crushed limestone that dissolves a little into the water and brings the pH up. No dosing, no power; the media is topped up over time.
pH and alkalinity Listen to the episode
UV steriliser
Tank water, borehole water and rainwater that will be drunk; any E. coli or coliforms on a certificate.
A stainless chamber with a lamp in a quartz sleeve; water passes the lamp and the dose kills what is in it. Size it on the flow quoted at 40 mJ/cm² (NSF Class A), not the higher flow quoted at 30 mJ/cm² on the same sheet. It wants clear water: 5 micron ahead of it, iron under 0.3 mg/L, hardness under about 120 mg/L or a softener first, turbidity under 1 NTU. The water around the sleeve also carries the lamp's heat away, so a chamber that holds air or drains cooks the lamp and shortens its life. Mount it vertically with the inlet at the bottom and the outlet at the top, or horizontally with both ports facing up; either way the chamber stays full and air leaves through the outlet. Close to the point of use, room to pull the sleeve, lamp changed yearly whether or not it still glows.
Why a 5 micron prefilter ahead of UV is mandatory UV dose explained Listen to the episode

What to leave behind, and what to check on a callback

Most callbacks are not equipment failures. They are a customer who was never shown what was installed, or a cartridge nobody could tell was full. Ten minutes at handover saves the trip.

Have this to hand

The water result the job was sized on, with the sampling point and date on it.
Model and serial off every unit: housing size, cartridge references, vessel and media, valve model, UV model and lamp reference.
The measured flow and pressure you sized on, and what the gauges read on the day of commissioning.
The manufacturer's own service instructions, handed over rather than left in the box.

What a change usually means

Pressure complaint a few months after handover: Almost always the sediment cartridge doing its job. If you fitted gauges either side and showed the customer the starting numbers, this is a phone call rather than a site visit.
System blocked solid right after a cartridge change: Check the end-type cartridges first: an axial cartridge fitted upside down seals the housing shut. The open centre with the O-ring faces up.
Softener stopped softening: Salt first: empty tank or a bridged crust. Then whether the valve is completing its cycle and whether the drain is clear.
UV lamp still lit but the water fails a test: Output falls long before a lamp goes dark, and a fouled sleeve throttles the dose just as effectively. Check the lamp age, the sleeve and the prefilter before suspecting the unit.

What to send us

What the customer reports, at which taps, and whether it is hot, cold or both.
The gauge readings now against the commissioning numbers.
When the consumables were last changed and with what.
A photograph of the installation as it stands, labels legible.

Service intervals, cleaning methods and replacement parts come from the manufacturer's instructions for your actual equipment. What is here helps you notice a change and describe it accurately; it does not replace that documentation, and it is not a substitute for the installer where the work needs one.

How the units work

Four animations that answer the questions customers ask you on site. Switch the state and watch the water.

Two ways water moves through a cartridge, and which way up it goes

The shape of the cartridge decides the path, what the cartridge is good at, and whether the way you drop it into the housing matters.

Sediment cartridges and carbon blocks work radially: water fills the sump around the cartridge, passes through the wall from the outside to the hollow core, and leaves up the core through the head. The cartridge is hollow right through and the same at both ends, so it goes into the housing either way up. Direction does not matter.

Read the full guide

A UV steriliser: vertical or horizontal, right and wrong

Both ports sit on the same side of the chamber. Mounted right, the chamber stays full of water; mounted wrong, it holds air or empties itself. The water also cools the lamp: with the chamber empty, the lamp's heat has nowhere to go, it overheats and its life is cut short.

Chamber vertical, inlet at the bottom port, outlet at the top. Air leaves through the outlet, the chamber stays full and every litre rises past the whole lamp. The 5 micron cartridge ahead of it keeps the sleeve clean; leave room above to pull the sleeve out.

Read the full guide

An FRP vessel and its valve: service, backwash, rinse

The multiport valve on top of the vessel is what makes a media filter clean itself.

Raw water enters through the valve, spreads over the bed and flows down through the media. The bottom strainer collects it, it rises up the riser tube and leaves at the outlet. The dirt stays in the top of the bed.

Read the full guide

A softener and its brine tank: the regeneration cycle

The resin does the softening; the brine tank is how it gets its sodium back.

Hard water flows down through the resin beads. Calcium and magnesium stick to the beads and sodium comes off in their place; soft water rises up the riser to the house. The beads slowly fill up with hardness.

Read the full guide

Things people hear that are not true

The ones we correct most often.

A bigger micron number catches more.
The other way round. 5 micron is finer than 20. Coarse first, fine after, or the fine one blocks in a week.
A carbon filter makes water safe to drink.
Carbon removes taste, smell and chlorine. It removes no bacteria, no hardness and no salt. Germs need UV or UF; salt needs RO.
UV works on any water.
UV needs clear water. Turbidity and iron shield the germs and coat the sleeve. A 5 micron cartridge ahead of it is not optional.
Housings can be mounted any way that fits.
Vertical, sump down, arrow in the flow direction. Sideways they trap air, leak at the O-ring and bypass the cartridge.
A UV can lie any way that fits.
Horizontal is fine with both ports facing up, so the chamber stays full. Ports down and it can empty itself: the lamp runs dry and hot, and air sits along the top where part of the flow misses the dose. Vertical, inlet at the bottom and outlet at the top, is still the best install.
A softener needs no drain.
It backwashes and rinses brine to drain every regeneration. A drain with an air gap, and a place for the brine tank, are part of the quote.
RO is just a better filter.
It is a membrane that needs pressure, a drain for the reject and a tank; it takes the salt out and the taste with it. Right for brak water at the kitchen tap, wasteful as a whole-house default.
Cartridges last a year.
They last until the pressure drop says otherwise. As a guide, sediment three to six months, carbon six to twelve, a UV lamp twelve, an RO membrane two to three years; a gauge on each side of the set tells the customer when, and on a borehole it can be weeks.

The questions we get asked

Short answers. Every one ends in a next step.

Which filter do I sell for a customer who just wants nicer tap water?

On municipal water, a carbon block under the counter with its own tap. It takes the chlorine and the taste out and leaves the minerals in. Add UF if they store water in a tank; go to RO only if the water is brak.

GAC versus carbon block

What order do the housings go in?

Coarse to fine, then carbon, then anything delicate: 20 micron sediment, 5 micron sediment, carbon, then UF, RO or UV. Each stage protects the next; reversed, the fine one blocks first and the carbon fouls.

Why filters go coarse to fine

10 inch, 20 inch or Big Blue: how do I choose the housing?

On flow. A 10 inch 2.5 inch cartridge is a single-tap or small-flat device; 20 inch holds about twice the media, so it runs about twice as long on the same water; Big Blue (4.5 inch diameter) carries a whole house at 20 to 40 L/min with a sensible pressure drop. Polypropylene for cold water indoors, stainless where it is hot, exposed or commercial; clear sumps only out of the sun, or they grow algae. Ports here are BSP; imported American housings are NPT and the two do not mate.

Choosing a filter housing

What size FRP vessel and which valve?

Vessels are sized on the flow and the media's linear velocity, not on the house. The vessel and valve selector on this site takes the flow and the media and returns the smallest FlowShell vessel and the Runxin valve that can backwash it. Filter valves and softener valves are not interchangeable.

Filter valves versus softener valves

How big must the drain be for a backwashing vessel?

Backwash flow is two to three times the service flow and it arrives all at once: the valve wants at least a 13 mm drain line, 19 mm above about 26 L/min or a run over 6 m, the valve higher than the drain, and an air gap of twice the pipe diameter, never a sealed connection to the sewer. A drain that cannot take the flow means the media never lifts and never cleans.

Backwashing explained

How much salt does a softener use, and how often does it regenerate?

It depends on the hardness and the volume used: the resin holds a fixed amount of hardness per litre, and the valve regenerates when that is used up. A metered valve counts the litres; a time-clock valve guesses. Coarse softener salt, not rock or granulated; keep the brine tank a third to two-thirds full, above the water line, so a salt bridge cannot form, and never let it run dry. Softened water carries a little sodium, so bypass the garden and, if the customer prefers, the kitchen cold tap.

Softener sizing basics

Which way up does the UV go, and why does it matter?

Vertical, inlet at the bottom port and outlet at the top, both ports on the same side of the chamber: air leaves through the outlet and the chamber stays full. Where there is no height, horizontal is fine with both ports facing up. Ports down, or vertical with the water going in at the top and out at the bottom, and the chamber can drain itself when the flow stops; the lamp runs dry and hot, and the air it holds means part of the flow misses the dose.

UV dose explained

Does an RO need a drain and a pump?

A drain, always: a conventional unit sends three or four litres to drain for every litre it makes, through a saddle on the waste pipe above the trap. A pump only if the supply pressure is under about 3 bar or the customer wants a faster fill; a pressure-reducing valve above about 5.5 bar. Discard the first tank, and fit the tank where it can be reached for a membrane change.

How reverse osmosis works

What happens to the UV during load-shedding?

The water keeps flowing and nothing is treating it. Fit a normally-closed solenoid valve on the UV outlet that shuts when the power or the lamp fails, or run the ballast from the inverter. After a long stand with no flow the water in the chamber can be hot; let it run off. The same applies to a UV on a tank: put it after the booster pump, never on the pump's suction side.

What UV does and does not do

The borehole customer only wants cartridges. Can I do that?

You can, and you will be back in a month. Sand and iron on a borehole belong in backwashing vessels; cartridges after them polish. Sell the vessel and the valve, or explain why the cartridges will block.

How a media filter works

What goes wrong most often on site?

Housings on their side, cartridges in the wrong order, no bypass, no gauges, UV with the ports down or without a prefilter, a softener drain without an air gap or a brine tank never refilled, an RO without a working drain, a vessel whose backwash flow the pump cannot deliver, a clear housing in the sun, and a valve that was soldered to after it was fitted. Every one is a callback.

The commissioning faults we see most

What should I ask the branch for?

Send the water result (or the on-site readings), the flow in litres per minute, the pressure, and what the customer wants fixed. The branch returns product codes, sizes and lead times. We do not publish prices; when the catalogue opens, every line will show its lead-time band and stock status.

Talk to a person

Phone or WhatsApp the branch nearest you. Send a photo of your water certificate and we will tell you what we see. We quote from your analysis and your flow, and we do not publish prices.

Cape Town

5 Firgrove Way, Firgrove Industrial Estate, Macassar, 7134

+27 21 851 0133

Mon to Thu 08:30 to 16:30, Fri 08:30 to 16:00

sales@definitivewater.co.za

Johannesburg

Unit 067, Inospace Allandale Exchange, 917 Morkels Close, Halfway House, Midrand, 1685

+27 75 084 5743 WhatsApp Johannesburg

Mon to Thu 08:30 to 16:30, Fri 08:30 to 16:00

salesjhb@definitivewater.co.za

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Guides, episodes and calculators

The knowledge-base guides installers use most, each with a podcast episode, in English and Afrikaans.

All the episodes All the guides

Vessel and valve selector Vessel media fill Media filter sizing Hardness converter Runxin valve codes Unit converter

Treatment train designersoon

Type in your certificate and get a suggested treatment train. Opening soon, as a calculator, not a guarantee.

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Written by the Definitive Water Technologies team and technically reviewed by Chandré Naudé, BEng (Civil), 15 years in the water treatment industry.

General guidance for South African residential and light-commercial installations. Sizes and stages follow from the water and the flow; a test result and a branch conversation come before any purchase, and the branch confirms the exact product codes.

These guides are general information, compiled from published standards, manufacturer data and our own experience, and we keep them as accurate as we can. They are not a design, a specification or advice for a particular site. Whoever specifies, installs or operates a system, whether an engineer, an installer, a farmer or a plant manager, remains responsible for checking that what is written here applies to their water and their installation, and for the work itself. Definitive Water Technologies accepts no liability for errors in these pages or for work done on the strength of them. When in doubt, send us the analysis and talk to the branch.

The right filter, first time.

Start here: what is the job?

Whole-house filtration on municipal water

What is usually wrong

What to test, and what the numbers mean

Read these first for this job

The rest of the checklist

What fixes it

Sediment cartridge in a housing

Activated carbon: GAC or carbon block

Three-stage whole-house set

Water softener with a brine tank

UV steriliser

Pressure-reducing valve ahead of the set

Under-counter drinking water

What is usually wrong

What to test, and what the numbers mean

Read these first for this job

The rest of the checklist

What fixes it

Activated carbon: GAC or carbon block

Ultrafiltration cartridge

Under-counter reverse osmosis

Basic borehole filtration

What is usually wrong

What to test, and what the numbers mean

Read these first for this job

The rest of the checklist

What fixes it

FRP vessel with a backwashing valve

Iron and manganese vessel

Water softener with a brine tank

UV steriliser

Under-counter reverse osmosis

Rainwater tank filtration

What is usually wrong

What to test, and what the numbers mean

Read these first for this job

The rest of the checklist

What fixes it

Roof and tank kit: screens and first flush

Sediment cartridge in a housing

Activated carbon: GAC or carbon block

Calcite for sour water

UV steriliser

What to leave behind, and what to check on a callback

Have this to hand

What a change usually means

What to send us

How the units work

Two ways water moves through a cartridge, and which way up it goes

A UV steriliser: vertical or horizontal, right and wrong

An FRP vessel and its valve: service, backwash, rinse

A softener and its brine tank: the regeneration cycle

Things people hear that are not true

The questions we get asked

Talk to a person

Cape Town

Johannesburg

Guides, episodes and calculators