Data · storage
What size water tank do you need for outages? Litres by household and days
When the municipal supply stops for a day or three, a tank decides whether the toilets still flush. How big it has to be depends on three numbers: how many people, how many days, and how hard you are willing to save. We worked it out for three levels of use, from the bare minimum to a normal household.
By Borehole Payback · updated 4 November 2026
What our numbers show
Our calculation; 25 litres a person a day is the basis of the national free basic water allowance, 50 litres was Cape Town's Level 6B restriction in 2018
- For the essentials, drinking, cooking and basic washing, plan on 25 litres a person a day, the amount the national free basic water allowance of 6 kl a month is built on. A household of four needs 100 litres a day.
- If you also flush toilets with a bucket and shower briefly, plan on 50 litres a person a day, the limit Cape Town set at the height of its 2018 drought: 400 litres for four people over two days.
- Carrying on as normal, about 125 litres a person a day indoors, takes 1 500 litres for four people over three days. A 2 500 l tank covers five days of normal use for four people, or more than a week at 50 litres a person.
- A tank only helps if it is full when the outage starts and can be reached when the pressure drops: it needs a float valve on the municipal line and, for taps upstairs or a geyser, a small pressure pump.
A household of four, by days without water
| Without municipal water | Essentials, 25 l a person a day | Cape Town 2018 limit, 50 l | Normal use, 125 l |
|---|---|---|---|
| 1 day | 100 l, 500 l tank | 200 l, 500 l tank | 500 l, 500 l tank |
| 2 days | 200 l, 500 l tank | 400 l, 500 l tank | 1 000 l, 1 000 l tank |
| 3 days | 300 l, 500 l tank | 600 l, 750 l tank | 1 500 l, 1 500 l tank |
| 5 days | 500 l, 500 l tank | 1 000 l, 1 000 l tank | 2 500 l, 2 500 l tank |
| 7 days | 700 l, 750 l tank | 1 400 l, 1 500 l tank | 3 500 l, 5 000 l tank |
Litres for four people, rounded up to the next common tank size (500, 750, 1 000, 1 500, 2 000, 2 500, 5 000 or 10 000 l). Plan for a little more than the table: the outlet sits above the bottom of the tank, so the last few centimetres of water cannot be drawn off.
Two days, by household size
| Household, two days | Essentials, 25 l | 50 l | 125 l |
|---|---|---|---|
| 1 person | 50 l, 500 l tank | 100 l, 500 l tank | 250 l, 500 l tank |
| 2 people | 100 l, 500 l tank | 200 l, 500 l tank | 500 l, 500 l tank |
| 3 people | 150 l, 500 l tank | 300 l, 500 l tank | 750 l, 750 l tank |
| 4 people | 200 l, 500 l tank | 400 l, 500 l tank | 1 000 l, 1 000 l tank |
| 5 people | 250 l, 500 l tank | 500 l, 500 l tank | 1 250 l, 1 500 l tank |
| 6 people | 300 l, 500 l tank | 600 l, 750 l tank | 1 500 l, 1 500 l tank |
The three levels of use
- 25 litres a person a day covers drinking, cooking, washing hands and a strip wash. It is the figure behind the national free basic water allowance: 6 kl a month for a household of eight. Toilets are not flushed from the tank at this level.
- 50 litres a person a day was Cape Town's Level 6B restriction from February 2018. It allows a short shower or a bucket bath and flushing the toilet with grey water or a bucket.
- 125 litres a person a day is our model's normal indoor use, 15 kl a month for four people, as on the water tariffs page. It does not include the garden.
Setting the tank up
For outages the tank is fed from the municipal connection through a float valve, so it refills by itself when the supply comes back. A gravity tank on a stand can feed ground-floor taps; for showers, upstairs bathrooms or a geyser it needs a pressure pump, and a pump needs power, so during load-shedding that means a small inverter or a gravity line. If you also have a borehole, it can top the tank up during long outages; keep that plumbing separate from the municipal pipes, see borehole rules.
Drinking water stored for more than a few days should come from the municipal supply, be kept in a closed, opaque tank, and be used and refilled regularly.
Questions owners ask
How many litres of water does a person need per day?
For drinking, cooking and basic hygiene, about 25 litres; that is what the national free basic water allowance of 6 kl a month for a household of eight is based on. Cape Town's 2018 drought limit was 50 litres a person a day, including toilet flushing. Normal indoor use in a house with a modern toilet and shower is closer to 125 litres.
What size water tank do I need for a family of four?
For two days without municipal water at 50 litres a person, 400 litres, so a 500 l tank. For three days of normal use, 1 500 litres, so a 1 500 l tank. Size up if outages in your area last longer, or if a borehole is meant to refill the tank.