Water Tank / JoJo Sizing Calculator — South Africa
Calculate the right water storage tank capacity for municipal backup or rainwater harvesting. Standard JoJo tank sizes, pump notes, and installation guidance.
Quick answer: The DWS standard for South African household water consumption is 150 litres per person per day. A 4-person household wanting 3 days of water security during supply interruptions needs 4 × 150L × 3 days = 1,800 litres minimum — making a 2,500-litre JoJo tank the most common household choice.
⚠️ For planning purposes only. Water tank installations connecting to house plumbing must be done by a registered plumber. Rainwater for drinking must be filtered and treated.
How to Use This Calculator
- Enter occupants — number of people relying on the stored water.
- Adjust daily usage — default is 150L/person/day (DWS urban standard).
- Select days of autonomy — how many days you need if supply is cut.
- Choose intended use — full household, sanitation only, garden, or rainwater harvesting.
- Click Calculate — results show tank size, number of tanks, pump sizing, and days of supply.
Water Storage for South African Households
Water security has become a significant concern for South African property owners. Municipal water supply interruptions — from infrastructure failures, drought restrictions, and load shedding affecting pump stations — can leave households without water for days. A properly sized water storage tank provides essential resilience.
The Department of Water and Sanitation (DWS) urban standard is 150 litres per person per day for full domestic use including drinking, cooking, bathing, toilets, and laundry. For planning a backup tank, this figure combined with your desired days of autonomy gives you the minimum required storage volume.
Standard JoJo Tank Sizes in South Africa
JoJo Tanks is the dominant manufacturer in South Africa. Their tanks are made from LLDPE (food-grade plastic), UV-stabilised, and available nationwide. Standard sizes are:
- 500L: Garden irrigation, small backup — R800–R1,500
- 1,000L: 1–2 person short-term backup — R1,500–R2,500
- 2,500L: Most popular residential choice — R3,000–R5,500
- 5,000L: Family backup 5+ days or rainwater primary — R5,500–R9,000
- 10,000L: Large property / small farm — R9,000–R16,000
- 20,000L: Farm, smallholding, commercial — R18,000–R30,000+
Rainwater Harvesting in South Africa
Rainwater harvesting collects water from roof surfaces during rainfall for storage and later use. The collection formula is: Annual collection (L) = Rainfall (mm) × Roof area (m²) × Runoff coefficient. Typical runoff coefficients: IBR/metal roof: 0.85; clay/concrete tile: 0.80; thatch: 0.60.
| Province | Avg Annual Rainfall | Monthly Average | Dry/Wet Season |
|---|---|---|---|
| KwaZulu-Natal | 1,009mm | ~84mm | Summer rain |
| Mpumalanga | 635mm | ~53mm | Summer rain |
| Gauteng | 713mm | ~59mm | Summer rain (Oct–Mar) |
| Free State | 528mm | ~44mm | Summer rain |
| Western Cape | 515mm | ~43mm | Winter rain (May–Sep) |
| Eastern Cape | 437mm | ~36mm | Year-round |
| North West | 450mm | ~38mm | Summer rain |
| Limpopo | 467mm | ~39mm | Summer rain |
| Northern Cape | 175mm | ~15mm | Low / semi-arid |
Tank Installation Requirements in South Africa
Water tanks connected to household plumbing must be installed by a registered plumber. The connection requires a backflow prevention device — typically a double-check valve — to prevent contaminated tank water from flowing back into the municipal supply. This is a requirement under SANS 10252 and most municipal by-laws. Non-compliance can contaminate the municipal supply and the property owner may be held liable. Do not connect a tank to your plumbing without a registered plumber confirming the correct backflow protection is in place.
Tank positioning affects usable pressure. A tank elevated 1 metre above the outlet produces approximately 10 kPa of static pressure — barely enough for a toilet cistern. For gravity-fed systems to work, the tank must be elevated 3–5 metres above the highest outlet. A pressure pump (R1,500–R4,000) delivers consistent pressure regardless of tank height — the more practical solution for most South African residential installations where elevation is constrained by site conditions.
Water Quality and Treatment for Stored Water
Stored water in above-ground tanks is susceptible to algae growth, sediment, and bacterial contamination. Food-grade LLDPE tanks such as JoJo's standard range are UV-stabilised and opaque to minimise algae, but unsealed tanks can admit insects and runoff contamination. Always fit a sealed lid, a fine-mesh first-flush diverter on rainwater inlets, and an overflow pipe directed away from the foundation. For tanks storing water used for drinking or food preparation, filtration and UV sterilisation are essential — rainwater is not potable without treatment regardless of how clean the catchment appears. Municipal top-up connections to rainwater tanks must also be managed carefully — a float valve that tops up the tank from the mains supply must be fed through a break tank or air gap to prevent backflow, and the water in a mains-topped tank is no longer classified as municipal supply once it has entered the tank, meaning it must be treated before consumption. SANS 241 sets the national standard for drinking water quality in South Africa. Stored tank water does not meet SANS 241 without treatment unless it comes from a consistently clean municipal source, has been stored for less than 48 hours in a sealed food-grade container, and shows no signs of algae or sediment. For longer storage periods or any rainwater use, a basic treatment train of sediment filtration, activated carbon filtration, and UV sterilisation is the minimum recommended before consumption. JoJo Tanks recommends draining, scrubbing, and sanitising storage tanks with a food-grade chlorine solution every two years — more frequently in warm climates where bacterial growth accelerates.