Knowledge base

Water quality fundamentals

The chemistry every other decision refers back to: TDS, hardness, pH, chlorine, scaling indices and solids measurement.

Prefer listening? This section is also a podcast episode.

• TDS, EC and what conductivity actually tells you

  Total dissolved solids and electrical conductivity are the first numbers on any water analysis. Here is what they measure, how they relate, and what they cannot tell you.

• Water hardness: what it is and how it is measured

  Hardness is dissolved calcium and magnesium — the minerals behind scale in geysers, kettles and membranes. The units are the confusing part; the chemistry is simple.

• pH and alkalinity — and why they are not the same thing

  pH says how acidic the water is right now; alkalinity says how hard it will fight you when you try to change that. Confusing the two is the most common water chemistry mistake.

• Scaling and corrosion indices (LSI and RSI) in plain language

  The Langelier and Ryznar indices condense pH, hardness, alkalinity, temperature and TDS into one number that predicts whether water will deposit calcium carbonate or dissolve it. That is a scaling question, not a corrosion rate.

• Turbidity, SDI and suspended solids

  Three different ways of measuring the "dirt" in water — and why the one on the municipal certificate is not the one that protects an RO membrane.

• Chlorine: free versus total, and why downstream equipment cares

  The difference between free and total chlorine decides whether water is properly disinfected — and whether it is about to destroy an RO membrane.

Sediment filtration

Cartridges and housings: micron ratings, cartridge construction, carbon options, housing materials and staging.

Prefer listening? This section is also a podcast episode.

• Micron ratings: nominal versus absolute, and when the difference matters

  A "5 micron" cartridge can mean two very different things. Knowing which one you are buying decides whether the equipment behind it is actually protected.

• Spun-bonded, string-wound and pleated cartridges compared

  The three sediment cartridge constructions solve the same problem three different ways. Duty, solids load and budget decide which one belongs in the housing.

• GAC versus carbon block for chlorine, taste and odour

  Both cartridges use activated carbon; they package it differently, and the packaging changes contact time, pressure drop and what else the cartridge removes.

• Choosing a filter housing: polypropylene versus stainless steel

  The housing outlives many cartridges, so its material, pressure rating and format deserve more thought than they usually get — including which stainless grade the duty actually needs.

• Why filters are sequenced coarse to fine

  Staging filtration from coarse to fine is the cheapest reliability upgrade in water treatment. The reasoning is simple economics about where dirt should be caught.

• When to replace a filter cartridge (differential pressure, not the calendar)

  Cartridges are exhausted by dirt, not by time. Differential pressure is the honest gauge for sediment cartridges — with two important exceptions where the calendar rules.

Media filtration

Sand, glass, carbon and catalytic media beds: how they work, how they differ, and what backwashing demands.

Prefer listening? This section is also a podcast episode.

• How a media filter actually works: linear velocity, bed depth and freeboard

  A media filter is not a sieve — it is a bed of particles doing depth filtration, and three design numbers decide whether it works or merely looks like it does.

• Filter media compared: sand, glass (generic vs AFM) and anthracite

  Sand is the benchmark, glass media promise more — but "glass" covers two very different products — and anthracite is a team player. What each grain actually does in the bed.

• Catalytic media for iron and manganese removal

  Dissolved iron and manganese pass straight through ordinary filters. Catalytic media convert them to filterable solids in the bed — provided the conditions and the backwash are respected.

• Activated carbon: coal, coconut shell and macadamia shell compared

  The raw material an activated carbon is made from sets its pore structure — and the pore structure decides which contaminants it removes well. The three main shells and coals, honestly compared.

• Backwashing: why, when, and what goes wrong

  Backwash is the half of media filtration that happens in reverse — and most long-term media filter failures are really backwash failures wearing a disguise.

Softening & ion exchange

How softeners work, sizing basics, regeneration control, and softening versus the alternatives.

Prefer listening? This section is also a podcast episode.

• How a water softener works

  Ion exchange in one vessel and a salt tank — a softener swaps the minerals that scale for one that does not, then uses brine to reset itself. The mechanism, plainly.

• Softener sizing basics: hardness load, resin volume and salt dose

  Sizing a softener is bookkeeping — hardness in, capacity held, salt spent. Three numbers and two checks produce a defensible selection.

• Time-clock versus volumetric softener control

  Two ways for a softener valve to decide when to regenerate — on the calendar or on the litres actually used. The premium for metering usually repays itself in salt.

• Softening versus anti-scale cartridges versus antiscalant dosing

  Three ways to stop scale — remove the hardness, condition it, or hold it in solution. They are not interchangeable; each defends a different kind of equipment.

Reverse osmosis

Membranes, pretreatment, recovery and fouling — including the DuPont FilmTec family compared.

Prefer listening? This section is also a podcast episode.

• How reverse osmosis works: pressure, rejection and recovery

  RO pushes water backwards through nature's preferred direction. Three numbers — osmotic pressure, rejection and recovery — describe everything an RO system does.

• The DuPont FilmTec families: BW, LE/XLE, ECO, SW and the specialists

  DuPont's element names encode a design philosophy — rejection-first, energy-first, or duty-specific. A map of the families and how to choose between them.

• Why RO pretreatment is non-negotiable

  An RO membrane concentrates everything the feed brings to it. Pretreatment is not a cost around the membrane — it is the membrane's life-support system, and it has hard numbers.

• Fouling versus scaling: telling them apart, preventing both

  Both degrade an RO plant, but they are different diseases with different addresses, different symptoms and opposite cures. Diagnosing which one you have is half the repair.

• Membrane pressure vessels: end-port versus side-port, and the details that leak

  The vessel is the least glamorous part of an RO train and the source of a surprising share of its problems. Configuration, rating and seal discipline, explained.

• Permeate quality: what TDS to expect and why it drifts

  RO permeate is very good water, not perfect water — and its quality moves with temperature, recovery, pressure and time. What to expect, what is normal drift, and what is a fault.

UV disinfection

Dose, transmittance and lamp technology: what UV does, what it cannot do, and LED versus mercury lamps.

Prefer listening? This section is also a podcast episode.

• UV dose explained: flow, transmittance and end of lamp life

  A UV system is sized by dose, and dose is intensity multiplied by time. Every honest UV specification is built from the flow rate, the water's transparency and the lamp's worst day.

• What UV does — and what it does not do

  UV is a superb disinfection barrier and a terrible everything-else. Knowing exactly where its job ends prevents the two classic misapplications.

• UV versus chlorination — and when you need both

  The two mainstream disinfection routes are not rivals so much as specialists — one is a barrier, the other a bodyguard. The deciding question is what happens to the water after treatment.

• Why a 5 micron prefilter ahead of UV is mandatory

  Particles shadow microorganisms from the lamp, and the pathogens that matter most are the size that hides best. The cheapest component in the system is the one that makes the expensive one work.

• LED UV versus traditional mercury lamp UV

  UV-C LEDs are genuinely arriving in water treatment, and genuinely not ready to replace mercury lamps everywhere. An honest account of where each technology wins today.

Chemical dosing

Metering pump types compared, sizing rules, chemical compatibility and injection-point practice.

Prefer listening? This section is also a podcast episode.

• Metering pump types: solenoid, motor-driven diaphragm and peristaltic

  Three honest technologies for pushing small, precise chemical flows against pressure — each with a duty range where it is the obvious choice and edges where it is the wrong one.

• Sizing a dosing pump: the arithmetic and the 20–80% rule

  Dosing pump selection is one formula and one discipline — calculate the true duty point, then make sure it lands in the middle of the pump's range, against the real pressure.

• Chemical compatibility: heads, seals and the hypochlorite trap

  A dosing pump's mechanism rarely fails first — its wetted materials do. Matching head, seals and valves to the chemical is a five-minute check that prevents the commonest slow failure.

• Injection points, back-pressure valves and the syphoning fault

  Most dosing problems live at the two ends of the chemical's journey, not in the pump. How to build an injection point that doses what the pump meters — and nothing more.

Valves & system controls

Multiport valves, protection valves and the controls that keep vessels and pipework safe.

Prefer listening? This section is also a podcast episode.

• Multiport valves explained: what each position does

  The multiport valve is the brain and the plumbing of every media vessel in one device. Understanding its cycle positions turns a mysterious black box into a serviceable component.

• Filter valves versus softener valves — why they are not interchangeable

  They look identical on the vessel and share most of their cycle. The difference is the brine circuit — and fitting the wrong one costs either a broken process or money spent on nothing.

• Vacuum breakers: the small valve that stops big implosions

  FRP vessels and tanks are built to hold pressure in, not out. A vacuum breaker is the inexpensive air valve that protects them from the negative pressure that draining, cooling or siphoning can create.

• Solenoid, non-return and relief valves: where each belongs in a system

  Three small valves carry most of a water system's protection duties. Each has one job, a right location, and a characteristic way of being specified wrong.

Putting a system together

Treatment train sequencing, quick sizing rules and the commissioning faults seen most often.

Prefer listening? This section is also a podcast episode.

• The treatment train: what order components go in and why

  Water treatment components are sequenced by one principle — each stage protects the next and assumes the previous. The standard order, the reasoning, and the placements people get wrong.

• Quick sizing rules of thumb (and the calculators behind them)

  The first-pass numbers engineers carry in their heads, collected in one place — each with its limits stated and the site calculator that does the honest version.

• The commissioning faults we see most often

  The same dozen faults account for most warranty calls and most "the equipment doesn't work" conversations. A checklist of them, each with its telltale and its five-minute prevention.

Specialised applications

Water for industries with their own rules: food and beverage, pharmaceutical, laboratory, steam, and keeping a plant running when the municipal supply cannot be trusted.

• Food and beverage process water: what the regulations actually require

  In South African law, water used in a food premises means SANS 241 potable water — and audits expect you to prove it. What R638 says, where water fits in HACCP, and the treatment train that gets a plant there.

• Brewing and beverage water: alkalinity, chlorophenols and the RO-and-rebuild approach

  Beer and soft drinks are mostly water, and the water is a recipe ingredient. Why alkalinity is the number brewers fight, why trace chlorine ruins batches at parts-per-billion, and how bottlers specify their treated water.

• Food service water: coffee, combi ovens and ice

  The three water-hungry machines in every commercial kitchen fail for three different reasons. SCA coffee water targets, combi-oven chloride limits, and why the ice machine gets a carbon block.

• Pharmaceutical water: purified water, WFI and what SAHPRA expects

  Purified Water and Water for Injection are defined by pharmacopoeia limits and inspected against GMP. The grades, the standard generation train, and why the loop matters more than the still.

• Laboratory water grades: Type I to Type III, ISO 3696 and CLRW

  Lab water is graded, and the grades are not interchangeable. What the ASTM, ISO and CLSI specifications actually say, the RO-plus-polishing systems that produce them, and what to feed an autoclave.

• Boiler feed water: softening is the entry ticket, blowdown is the bill

  Steam boilers concentrate whatever the feed water brings. The published feed and boiler-water limits for shell boilers, when softening alone stops being enough, and why the AIA inspection is where poor water treatment gets caught.

• When the tap cannot be trusted: point-of-entry treatment for substandard municipal supply

  The Blue Drop data says almost half of SA supply systems fail microbiological compliance, and interruptions push dirt into the mains. The point-of-entry barrier train that lets a business stop caring what arrives.

• Backup water: tanks, boreholes and rain — and the treatment each one needs

  Day Zero taught South African business that a second water source is infrastructure, not paranoia. Sizing stored water, licensing and treating a borehole, and what it takes to make rainwater potable.

Agricultural water

Water on the farm, written for drought: boreholes under falling water tables, livestock and irrigation water quality, dams and rivers as a source, and the treatment that keeps drippers, dairies and pack-houses running.

• Borehole water in drought: when the water table drops

  A drought reaches your borehole months after it reaches your lands — and when it does, both the amount of water and the water itself change. Why last year's lab certificate stops describing the water, how to find out what a borehole can really give, and how to treat what comes up.

• Farm dams and rivers: mud, algae and making surface water safe

  Surface water is weather you can pump — clear one week, mud the next, and in a hot dry autumn it can grow something that kills cattle overnight. What turbidity and blue-green algae do, and the treatment steps that turn a dam into a reliable supply.

• Livestock drinking water: how much, how salty, and what poisons it

  A dairy cow in milk drinks five litres for every litre of milk she gives, and tolerates only a third of the salt a dry ewe shrugs off. The official South African numbers per species — how much water, how much salt, and the handful of real poisons — plus the trough habits that protect the herd.

• Reading an irrigation water analysis: salt, sodium and the toxic ions

  An irrigation analysis answers four questions — will the salt cost yield, will the sodium seal the soil, will an ion burn the crop, and will the water damage the equipment. The South African guideline numbers that answer each, in plain terms.

• Why drippers block: sand, lime, iron and slime

  A dripper's water passage is under a millimetre wide, and the crop guideline tolerates twenty-five times more iron than the emitter does. The clogging hazard numbers, the one-tenth filtration rule, choosing between screen, disc and media filters, and the chlorine-and-acid maintenance that keeps lines alive.

• Spray water: the most expensive water on the farm

  The few hundred litres in the spray tank carry the priciest chemistry on the farm — and hard, alkaline or muddy water quietly cancels it. How hardness ties up glyphosate, why some insecticides die in the tank within minutes, and what to test and fix before blaming the product.

• Fertigation: feeding through the water without wrecking it

  Injecting fertiliser through the irrigation system saves labour and puts nutrition exactly where the roots are — until calcium meets sulphate in a stock tank, or fertiliser siphons back into the borehole. Injection equipment compared, the mixing rules, and the backflow protection the law expects.

• Dairy water: the parlour is a food factory

  The law treats a milking shed as food premises, and the water that touches milk equipment must meet the drinking-water standard's microbiology. What the regulations actually require, why hard water grows milkstone, how iron eats your sanitiser, and the plate-cooler water worth catching.

• Poultry and piggery drinking lines: the biofilm war

  A broiler drinks nearly twice what it eats, through kilometres of warm plastic pipe that biofilm loves. The water-quality numbers for birds and pigs, the chlorine-and-pH discipline at the far nipple, and the between-flock line clean that decides the next cycle's performance.

• Pack-house wash water: where the audit meets the dump tank

  Export fruit is washed, cooled and moved in water — and the audit schemes treat every litre of it as food contact. What GLOBALG.A.P. and South African law require, how a recirculating dump tank is kept safe with chlorine and pH control, and why Listeria changed the rules for hydrocoolers.

• Drought-proofing the farm supply: storage, rain and the arithmetic of scarcity

  The agencies have already published the warning for 2026-27 — a strong El Niño and rising odds of a dry summer. How many days of water the farm should hold, what an open dam loses to the sky, what a shed roof can harvest, and the registrations that keep it all legal.