Water storage and septic tank sizing calculator
Indian norms budget about 135 litres per person per day for a house; overhead tanks hold one day, underground sumps two to three days where supply is intermittent (most of NCR). Septic tanks are sized per IS 2470 on users and a cleaning interval. The tool gives capacities and practical L × W × D dimensions.
- Overhead tank
- 675 L needed → buy 1,000 L (PVC/HDPE, 3-layer)
- Underground sump
- 1,350 L → RCC sump 1.16 m × 0.77 m × 1.5 m deep
- Septic tank capacity
- 1,500 litres (1.5 m³) for 5 users, 2-year desludging
- Septic tank size (two chambers)
- 1.22 m × 0.82 m × 1.5 m deep (first chamber two-thirds of length)
- Soak pit
- About 1.2 m diameter × 2.5 m deep dry-brick pit, 2 m from the tank, 10 m from any well
Copy link to this calculation · JSON API · Estimates only; verify rates with the source below.
How it is calculated
Daily demand = residents × litres per person per day (135 L for houses per IS 1172). Overhead tank = demand × days of storage, rounded up to the standard moulded size; underground sump = demand × days of backup. Septic tank capacity (simplified IS 2470) = 150 L per user of liquid retention + 30 L per user per year of sludge over the desludging interval, minimum 1,500 L; dimensions assume 1.5 m liquid depth and a 1.5:1 length-to-width ratio, with a soak pit for effluent.
Worked example
Five residents at 135 L: 675 L a day; a 1,000 L overhead tank for one day and a 1,350 L sump (≈ 1.16 × 0.77 × 1.5 m) for two days. Septic tank for 5 users with 2-year cleaning: 1,500 L, roughly 1.22 × 0.82 × 1.5 m internal, plus a soak pit.
Frequently asked questions
What size water tank for a family of 5?
About 675 litres a day; a 1,000 L overhead tank for one day's supply and a 1,000–1,500 L sump if municipal supply is intermittent.
How is septic tank size calculated in India?
Per IS 2470: liquid retention of about 150 L per user plus sludge storage of 30 L per user per year of the cleaning interval, with a minimum of 1,500 L for a house; two chambers, the first two-thirds of the length.
Is a septic tank allowed in Noida societies?
Group-housing societies are sewer-connected and use STPs, so no. Independent plots in unsewered villages and farmhouses use septic tanks with soak pits; keep 10 m from any borewell.
Sources and what to verify: IS 1172 water supply norms; IS 2470 septic tank design.
Estimates for planning only; not financial, legal or tax advice. Figures reflect common practice and published rates as of November 2026. Found an outdated rate? Email hello@zeorent.com.