Building a house or adding floors? Enter how many people will live there and how often water comes, and get the litres you use a day, the overhead tank size, the underground sump size in feet and a pump size, with a section drawing to show your plumber or contractor. Part of our free home planning tools.
How to use the water tank calculator
- Set the number of households (count each rented floor as one) and people in each.
- Pick the water per person per day. 135 L is typical for a home with flushing toilets.
- Choose how often water comes: every day, every two days, twice a week, weekly or tanker, or borewell only.
- Choose how much the overhead tank should hold (usually one day) and the number of floors.
- Read the tank, sump and pump sizes, the section drawing and the sump plan. Under More settings you can add garden watering, fix the sump width or depth, or change the floor height.
- Optionally mark the tank and sump positions for a Vastu check, then download a PNG, print or share the result.
Water Tank & Sump Calculator
Overhead tank, underground sump and pump size for Indian homes
More settings
How we got these numbers
Things to check
Vastu
Traditional guidance; schools differ. Shown for planning ideas only.
Educational estimate. Water use differs by household and city; tank sizes are rounded to common plastic tank sizes. The sump walls, base slab and waterproofing, and any tank stand on the roof, must be designed by an engineer. Follow your local authority's rules on water storage and distance from septic tanks.
How the calculator works
Daily need = people × litres per person per day, plus garden watering (about 5 L per m², or 0.5 L per sq ft) and any other use you add. 135 L per person is the figure commonly cited from the National Building Code and CPHEEO norms for homes with full flushing; bigger cities plan for 150–200 L.
The overhead tank holds half a day, one day or one and a half days of that, rounded up to a common plastic tank size (500, 750, 1000, 1500, 2000, 3000 or 5000 L), or two or three tanks when one is not enough.
The sump holds the water for the days between supplies plus half a day as a buffer: 1.5 days for a daily supply, 2.5 days for every other day, 4 days for twice a week and 7.5 days for a weekly tanker, rounded up to the next 500 L. Its inside size comes from the water depth (picked automatically between 3 and 5 ft so the sump stays at least about 4 ft wide), with 1 ft above the water for the inlet and an air gap.
The pump size assumes the overhead tank is filled in about 30 minutes, lifting water from the bottom of the sump to the tank inlet, with 20% added for pipes and bends and a pump set efficiency of about 45%.
Water tank size for your family (quick table)
At 135 L per person per day, with an overhead tank holding one day:
| People | Water a day | Overhead tank | Sump, daily supply | Sump, supply every 2 days |
|---|---|---|---|---|
| 2 | 270 L | 500 L | 500 L | 1000 L |
| 4 | 540 L | 750 L (1000 L is common) | 1000 L | 1500 L |
| 5 | 675 L | 750 L | 1500 L | 2000 L |
| 6 | 810 L | 1000 L | 1500 L | 2500 L |
| 8 (two families) | 1080 L | 1500 L | 2000 L | 3000 L |
| 12 (three families) | 1620 L | 2000 L | 2500 L | 4500 L |
Example: a 1500 L sump works out to about 4 ft × 4 ft inside with 3′6″ of water, plus 1 ft above the water. Outside, with 200 mm walls, plan about 5′3½″ × 5′3½″.
Overhead tank or sump: do you need both?
Where municipal water comes for a few hours a day or on alternate days, the sump stores the supply at low pressure and the pump lifts it to the overhead tank, which then feeds taps by gravity. With a reliable borewell alone, many houses skip the sump and pump straight to the roof tank. Keep the sump well away from the septic tank and soak pit, raise its top above the ground with a tight lid, and place the roof tank over beams or columns: a full 1000 L tank weighs about a tonne.
Water tank position as per Vastu
Commonly cited Vastu guidance places the overhead tank in the south-west of the terrace (west or south are acceptable) and avoids the north-east, east and south-east. The underground sump is preferred in the north-east, north or east, away from the south-west, south-east and the centre. These are traditional preferences and schools differ. The Vastu room advisor covers tank and sump positions by entrance direction, and the Vastu floor plan designer lets you place them on your plot.
Frequently asked questions
What size water tank do I need for a family of 4?
At about 135 litres per person per day, a family of four uses roughly 540 litres a day. A 750 litre overhead tank covers one day, and the very common 1000 litre tank covers almost two days. If municipal water comes daily, a sump of about 1000 litres (one and a half days) is enough; if it comes every other day, plan about 1500 litres.
How much water does one person use per day in India?
For homes with flushing toilets, about 135 litres per person per day is the figure commonly cited from the National Building Code and CPHEEO norms; larger cities plan for 150 to 200 litres. Households that use less (no flushing, bucket baths) can work with about 100 litres.
How do I calculate sump size?
Multiply the daily water need by the number of days the sump must last: the days between municipal supplies plus about half a day as a buffer. Divide the litres by 1000 to get cubic metres, then divide by the water depth (often 1.2 to 1.5 m) to get the floor area. Add about 300 mm (1 ft) above the water level for the inlet and air gap.
How many litres is a 1 cubic metre or 1 cubic foot tank?
One cubic metre holds 1000 litres and one cubic foot holds about 28.3 litres. A sump with 5 ft × 5 ft of floor and 5 ft of water holds 125 cubic feet, about 3540 litres.
What HP pump is needed for an overhead tank?
Most two- and three-storey houses manage with a 0.5 to 1 HP pump. The calculator estimates it from the tank size (filled in about 30 minutes) and the height the water must be lifted, including the sump depth and pipe losses. Ask your plumber to confirm with the pump maker’s chart.
Where should the water tank be as per Vastu?
Commonly cited Vastu guidance places the overhead tank in the south-west of the terrace (west or south are acceptable) and avoids the north-east. The underground sump is preferred in the north-east, north or east, away from the south-west and south-east. This is traditional guidance and schools differ.
Is a sump necessary if I have a borewell?
Not always. If the borewell pump can fill the overhead tank whenever needed, many houses skip the sump. A small sump is still useful if you also receive municipal or tanker water, or if the borewell yield is low and has to be stored.
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Related reading: sunk slab in bathrooms and waterproofing and parts of a building.
Sources and limitations
Per-person water figures are the values commonly quoted from the National Building Code of India 2016 (Part 9, Plumbing Services) and CPHEEO manuals; actual use varies widely. Sump days, tank sizes and the pump estimate are planning rules of thumb, not a plumbing design. Vastu notes are traditional guidance, not guaranteed outcomes. Report errors via our Corrections Policy; see our Editorial Policy and Methodology.
Disclaimer: Online educational publication only. Not a substitute for licensed architectural, structural, plumbing or legal services. Full disclaimer · contact@speakarch.com
Last updated: 8 November 2026