Why Rainwater Harvesting Makes Sense in South Africa
Water security is a real and growing concern for South African homeowners. Water restrictions during drought years, rising municipal water tariffs, and increasing frequency of supply interruptions have driven significant growth in domestic rainwater harvesting and water storage. A correctly installed rainwater tank system reduces your municipal water consumption, provides security during restrictions, and lowers your water bill over time.
Tank Types and Capacities
South African rainwater tanks are available in several materials:
- Polyethylene (LLDPE) tanks — the most common. UV-stabilised, food-grade, lightweight, and available in a wide range of sizes. Colours include green, black, and sand (darker colours reduce algae growth). Brands include JoJo, Roto, and others. Sizes: 500 to 10,000 litres. Most popular for residential use: 2,500 to 5,000 litres.
- Steel (corrugated galvanised) tanks — larger capacities, long lifespan, typically require a liner. More common for agricultural and large-scale storage.
- Concrete tanks — built in-situ; durable but expensive. Typically underground or semi-underground.
For a typical three-bedroom household, a 2,500–5,000 litre tank provides meaningful water security for toilet flushing, garden irrigation, and car washing during water restrictions. Larger households or those wanting to cover more uses will need multiple tanks or a higher capacity.
What a Good Installation Involves
- Gutters and downpipes — the tank is fed from roof runoff through gutters. Gutters must be clean and in good condition. A leaf filter at the downpipe prevents debris entering the tank.
- First-flush diverter — diverts the first flow of water after a dry period (which carries the most contaminants from the roof surface) away from the tank. A critical component that many low-cost installations omit.
- Tank base — the tank must sit on a firm, level base — concrete slab or compacted gravel. A full water tank is very heavy: a 5,000 litre tank weighs 5 tonnes. An unstable base causes the tank to deform over time and can damage fittings.
- Overflow provision — the tank must have an overflow outlet that directs excess water away from the foundation of the house.
- Pump and pressure system — for water to reach taps, toilets, and garden irrigation at pressure, a pump (automatic or booster) is required. A pressure pump with a pressure tank (R2,000–R6,000) provides consistent pressure. Gravity-fed systems (tank elevated above the outlets) work without a pump but require the tank to be positioned high.
- Water quality — rainwater harvested from roofs is not potable (not safe to drink) without treatment (sediment filtration plus UV sterilisation as a minimum). Clearly label and plumb non-potable water lines to avoid cross-contamination with municipal water.
Municipal Regulations
Most South African municipalities permit rainwater harvesting with some conditions. Common requirements: non-potable water must be clearly labelled, cross-connection with the municipal supply is prohibited, and overflow must not direct water onto public property or neighbouring plots. Check with your municipality before installation — regulations vary.
Choosing an Installer
Use a registered plumber (PIRB registered) for any tank installation that involves connections to your home's plumbing system. Get three written quotes specifying tank capacity, brand, pump model, first-flush diverter, base preparation, and any plumbing connections. Ask what experience the installer has with rainwater harvesting systems specifically — general plumbers may not be familiar with best practice for tank systems.