Free tool
Water Tank Size Calculator
Work out how big a water tank you need to ride out water outages or store rainwater, and how long common tank sizes will last your household.
How the calculator works
It multiplies your household's daily water use by the number of days you want covered, then picks the smallest standard tank that holds at least that much. Daily use comes either from household size and how carefully you use water, or straight from your municipal bill, which is the most accurate figure you have.
The four usage levels are planning presets, not measurements. The UN puts the water needed for most basic needs at 50 to 100 litres per person a day, and 50 litres was the limit Cape Town asked residents to keep to in 2018. Most households use more than that when water is flowing normally, so if you have a bill to hand, use it.
How long will a 5 000 litre tank last?
A family of four using about 150 litres each a day goes through roughly 600 litres a day, so a 5 250 litre tank lasts close to nine days. On essentials only, at 50 litres each, the same tank lasts more than three weeks. Halve the household or double the usage and the time halves with it.
JoJo tank sizes and dimensions
JoJo's vertical tanks are the most common sight in South African gardens. The sizes and dimensions below are as listed on jojo.co.za in October 2026. Check the current figures with your supplier before you plan the base or the space.
| Capacity | Diameter | Height |
|---|---|---|
| 260 litres | 670 mm | 940 mm |
| 500 litres | 840 mm | 1 080 mm |
| 1 000 litres | 1 110 mm | 1 300 mm |
| 1 500 litres | 1 410 mm | 1 200 mm |
| 1 800 litres | 1 200 mm | 1 780 mm |
| 2 000 litres | 1 420 mm | 1 450 mm |
| 2 400 litres | 1 420 mm | 1 700 mm |
| 2 700 litres | 1 420 mm | 1 860 mm |
| 4 750 litres | 1 820 mm | 2 060 mm |
| 5 250 litres | 1 820 mm | 2 255 mm |
| 5 500 litres | 1 900 mm | 2 240 mm |
| 10 000 litres | 2 200 mm | 3 150 mm |
| 15 000 litres | 2 600 mm | 3 260 mm |
| 20 000 litres | 2 600 mm | 4 270 mm |
JoJo is a trademark of its owner. Water Filter Systems is not affiliated with JoJo; the sizes are listed to help with planning.
What a backup tank needs to be useful
- A pump and pressure control so the taps, shower and geyser keep working when the mains are off.
- A sediment filter after the pump to catch grit before it reaches fittings and appliances.
- A UV steriliser if the stored water will be used for drinking, with sediment filtration ahead of it.
- A first flush diverter and screens on rainwater systems, covered in our rainwater filtration guide.
If you would rather have it planned for you, our home water filtration systems are sized around the tank, the pump and the water source.
FAQs
Water tank questions
How long will a 10 000 litre water tank last?
It depends on how much you use. At 150 litres per person a day, a family of four uses about 600 litres a day, so 10 000 litres lasts about 17 days. On essentials only (50 litres each), the same tank lasts around 50 days.
What size water tank does a family of four need?
For three days of everyday use at about 150 litres each, a family of four needs around 1 800 litres, so an 1 800 or 2 000 litre tank. For a full week, about 4 200 litres, so a 4 750 litre tank. Use the calculator above with your own numbers.
Can I drink the water from my tank?
Not without treatment. Stored water needs at least a sediment filter, and water for drinking needs a disinfection stage such as UV. Rainwater and borehole water also need testing first. Inside the City of Cape Town, the Water By-law restricts using alternative water for drinking without the City's approval, so check with the City first; elsewhere, check your municipality's by-laws. Our rainwater filtration guide covers the full treatment train.
How much rainwater can my roof collect?
Every millimetre of rain on one square metre of roof is one litre of water. A common planning figure is to expect about 80% of that in the tank after splash, evaporation and the first flush, so a 100 m² roof collects roughly 800 litres from a 10 mm rain day.
What are the most common JoJo tank sizes?
JoJo's vertical range runs from 260 litres to 20 000 litres. For household backup, the 1 000 to 2 700 litre tanks suit townhouses and smaller homes, while the 4 750 to 5 500 litre tanks are a common choice for family homes. The full list with dimensions is in the table above.
Related guides
Rainwater Filtration Guide: Tank Filters and Drinking Water
Rainwater filtration for Cape Town homes: is rainwater safe to drink, sizing a first flush diverter, choosing a water tank filter, UV and City rules.
Read Guide
Is Tap Water Safe to Drink in South Africa? (Cape Town Included)
Can you drink tap water in Cape Town? What SANS 241 and the latest Blue Drop results show for South Africa, why quality varies and when a filter helps.
Read Guide
How Water Filtration Systems Work: A Plain-English Guide
How water filtration systems work, stage by stage: what sediment, carbon, softeners, reverse osmosis and UV each remove, and why the order matters.
Read Guide
Want a tank setup that's ready to use?
Tell us your tank size and water source. We will plan the pump, filtration and UV so the stored water is usable when you need it.