Water Demand (NBC)
Water demand is the design daily water requirement of a building, computed from occupancy numbers and per-capita norms by use class per the NBC 2016 Part 9 / IS 1172 basis — the root number behind tank, pump, main and STP sizing.
Why it matters on an MEPF project
Everything hydraulic descends from this one calculation: raw and domestic tank volumes, transfer and hydro-pneumatic pump duties, municipal-connection sizing, and the sewage figure that sizes the STP. Get demand wrong and every downstream system inherits the error in concrete and pipework.
The craft is in honest occupancy and use classification — factory workers vs office staff vs residential occupants carry different norms; visitors, canteens and process water ride on top; and phased occupancy argues for staged tankage. Storage split (underground raw vs overhead domestic vs the fire reserve, which is separate and sacrosanct) then turns litres into structures the plan-sanction authority checks.
How it's specified in practice
| Parameter | Typical / working position | Governing reference |
|---|---|---|
| Norm basis | Litres/person/day by occupancy class | NBC 2016 Part 9 / IS 1172 |
| Add-ons | Canteen, process, visitors, landscaping | design additions |
| Storage split | UG raw + OH domestic (+ separate fire reserve) | NBC practice |
| Downstream | Sewage fraction → STP; peaks → pump duties | design chain |
Common mistakes
- One blended norm for a mixed-use building.
- Fire reserve conflated with domestic storage.
- Process water guessed rather than metered/specified.
- No diversity between total demand and instantaneous pumping duty.
Related on this site
One of 68 working definitions in the MEPF & solar engineering glossary. The buying side of the same decisions is in the buyer's guides; the numbers are in the calculators.
Frequently asked
How much water does my building need per day?
Occupancy × the per-head figure that applies to each class, plus process and special uses. Our water-demand calculator adds up the figures you enter and gives operational storage; the approved PHE design fixes the final numbers, and fire storage is kept separate.
Do norms differ for factories vs offices?
Yes — the per-capita basis differs by use class, and factories often add process and canteen loads that dwarf the human norm. Classify honestly before calculating.
Standards referenced: NBC 2016 Part 9 · IS 1172