Household water tank sizing
Persons × days of storage × litres per person per day, then round up to a standard tank size.
The sizing norm comes from IS 1172:1993 (Code of Basic Requirements for Water Supply, Drainage and Sanitation): it recommends 150–200 litres per head per day for residences with full flushing systems, with 135 lpcd retained as the minimum for LIG/EWS housing — and 135 lpcd is the figure CPHEEO and most municipal planners use as the standard urban norm. Of that, roughly 45 L is flushing and the rest covers drinking, cooking, bathing and washing.
Practical notes: round up, not down — the next standard size costs little more and covers guests and supply gaps. And remember the structural load: water is 1 kg per litre, so a 1000 L tank puts roughly a tonne on the slab or staging.
FAQ
How many litres of water does a family of 4 need per day?
At the 135 lpcd planning norm, 540 litres per day — so a 750 or 1000 L tank covers one day with margin. Full-flush urban homes sized at 150–200 lpcd need 600–800 L/day.
Why size for more than one day?
Municipal supply in many Indian cities runs intermittently; one to two days of storage is the practical norm so the overhead tank bridges supply gaps.
Is 135 litres per person an official figure?
Yes — see the note below for exactly what IS 1172:1993 says and where 135 vs 150–200 lpcd applies.