Rainwater harvesting filtration

Rainwater harvesting has moved from green gesture to core supply strategy across South Africa — driven by municipal interruptions, tariff escalation and water-security planning. The water itself starts clean but collects what the roof and gutters hold: dust, leaf litter, insect debris and bird droppings, then sits in a tank where organics decay. Untreated, stored rainwater develops colour, odour and a microbiological load that disqualifies it from anything beyond garden use.

Treatment is staged and unglamorous. First-flush diversion and leaf screens at the tank inlet do more per rand than any downstream component and halve the load on everything after the pump. After the pump, a two-stage cartridge train — 20 micron washable pleated ahead of 5 micron spun polypropylene — removes the particulate that carries most of the contamination.

Colour, taste and odour from decayed organics are a carbon duty: a granular activated carbon or carbon block cartridge sized to the real draw-off flow, replaced on breakthrough (the return of odour is the field indicator) or on the cartridge's rated volume, whichever comes first.

Where the supply feeds bathrooms, kitchens or any potable point, UV disinfection is the final barrier — 30 mJ/cm² at the duty flow, downstream of 5 micron filtration, with annual lamp replacement at 9 000 hours. For whole-house duty, size the UV chamber on the pump's actual delivery, not the average consumption: dose is flow-dependent and the pump defines peak flow.

Every component — housings, cartridge sets, UV chambers, lamps and spares — is a stocked standard line in both branches, with replacement elements available ex-stock for the service cycle that keeps a rain system genuinely potable.