Water Storage: household sizing to rainwater math

Litres-first tools for overhead tanks and sumps, IS 1172 household sizing, and the harvesting arithmetic — plus everything in gallons for US storage.

Storing water well is a sizing problem in two parts: how much you need, and where it lives. The Indian norm is 135 litres per person per day (IS 1172), so a family of four wants roughly 540 litres a day — and because municipal supply is often intermittent, most homes pair a larger underground sump for bulk storage with a smaller overhead tank for gravity pressure. Below: a litres-first calculator for any tank, household sizing built on the standard, rainwater-harvesting and septic tools, and the guide to splitting storage between overhead and underground. Everything works in gallons too for US storage tanks.

Water Storage: household sizing to rainwater math

Calculators

Capacity in litres

Household sizing (IS 1172)

Rainwater harvesting

Septic sizing

Sizes

1000 litre tank

2000 litre tank

All litre sizes

Guides

Overhead vs underground

Litres per person per day

Reference

Water weight — slab & staging loads

US gallon sizes