Water tank size calculator
A storage tank covers the times when the mains or a well can't supply enough. Its size is people × daily use × days of autonomy.
Your measurements
Result
- Recommended tank volume
- 600 L
For a home on mains water one day of autonomy is usually enough; areas with frequent interruptions may need more.
How the calculation works
- Volume (litres) = number of people × use per person per day × days of autonomy.
Worked example
A family of 4 using 150 litres per person per day, for one day of autonomy, needs 4 × 150 × 1 = 600 litres.
What the calculator assumes
- 150 litres per person per day is full household use: shower, toilet, cooking, laundry and dishes.
- The tank covers periods when the mains or the well can't supply enough.
When to adjust the result
- Garden watering or filling a pool is added separately — in summer it can exceed household use.
- The tank needs a booster pump for pressure, and water stored for a long time must be filtered and refreshed.
Choosing and placing a water tank
Size a storage tank for the days of autonomy you need, not just daily use: two or three days of consumption is a common target for a house with an unreliable supply. For rainwater, the usable volume depends on roof area and rainfall as well as on demand.
A full tank is heavy — 1,000 litres weighs a tonne — so it needs a level, load-bearing base. Keep drinking-water tanks opaque and covered to prevent algae, fit an overflow and a screened vent, and plan access for cleaning. Rainwater and well water must not be connected to the public drinking-water supply.
Frequently asked questions
What size water tank for a family of four?
About 600 litres for one day at 150 litres per person; more for several days or garden use.
How much water does one person use per day?
Typically 100–150 litres in a household, depending on habits and appliances.
Above-ground or underground tank?
Above-ground tanks are cheaper and easy to inspect but take space and can freeze; underground tanks keep water cool and frost-free but cost more to install.
Can I drink stored rainwater?
Not without proper treatment and testing. Untreated rainwater is suitable for the garden, WC flushing or washing machines where allowed.