Water tank & sump size calculator
Size the overhead tank and underground sump from who actually lives in the house: daily demand at the CPHEEO norm, your chosen days of storage, the nearest stocked tank size to buy, and sump dimensions that fit beside the house.
135 L/person/day is the CPHEEO domestic norm. Metro-water areas with reliable daily supply can run a smaller sump; borewell-only streets should size up.
Plan the tank into the house, not after it
A Plot2Plan floor plan places the overhead tank on the terrace level as a roof fitting — exempt from FSI, kept off the entry level, and checked by the same validator as every room. Generate a plan and this calculator pre-fills occupancy from its bedroom count.
Common questions
What size overhead tank for a family of 4?
At the CPHEEO norm of 135 litres per person per day, a family of four uses about 540 litres a day — so a 750 or 1,000 litre overhead tank gives a comfortable day's storage with headroom for guests and washing days. Tanks are stocked in standard sizes (500, 750, 1000, 1500, 2000 L…), so buy the next size up from your computed need.
How big should the underground sump be?
Two to three days of demand is the usual sizing where municipal supply is intermittent — for a family of five that is around 1,400–2,000 litres (1.4–2 m³). Streets on tanker or borewell supply should hold more. The calculator also lays the volume out as length × width × depth so you can check it fits a setback.
How much water does a person use per day?
The CPHEEO manual's domestic norm is 135 litres per capita per day with full flushing; 70 L covers a minimal no-flush pattern, and 150–200 L suits homes with gardens, car washing or generous fittings.
Where do the tank and sump go on the plot?
The overhead tank sits on the terrace, usually over the staircase mumty for head. The sump goes in a setback, commonly near the gate so the metro-water or tanker connection reaches it. On a Plot2Plan terrace level, the tank is a roof fitting the validator places rules around — it consumes no FSI.