City Water Demand Calculator
The water a city needs to supply — residential, non-residential, and the share lost to leaks — as daily, peak-day and annual volumes.
Demand at the tap is population times per-capita use, plus a non-residential share for industry and commerce.
How the city water demand calculator works
Demand at the tap is population times per-capita use, plus a non-residential share for industry and commerce. Demand at the source is larger, because a share of what is produced never reaches a customer: non-revenue water from leaks and unmetered use runs 10 to 30% in most systems.
The peak day is what the treatment plant is sized for, and it runs 1.5 to 2 times the average in a hot, dry climate.
Formula: source = (population × L/person + non-residential) / (1 − losses)
Worked examples
| Inputs | Average day at the source (ML) | Note |
|---|---|---|
| 180,000 people at 200 L | 57.18 | about 57 ML a day |
| A leaky network | 69.43 | a fifth more at the source |
| Water-efficient city | 40.02 | a much smaller plant |
FAQFrequently asked questions
How much water does a city use per person?
Two hundred to three hundred liters a day at the tap in most developed cities, before non-residential use and losses; efficient cities get under 150.
What is non-revenue water?
Water produced but not billed — leaks, bursts, firefighting and meter under-reading. Ten per cent is good; thirty is common in older networks.
Why size for the peak day?
Because a treatment plant that meets the average fails in a heatwave. Storage smooths the peak hour; the plant must meet the peak day.
What is a megaliter?
A million liters — an Olympic pool is about 2.5 ML. A gigaliter is a thousand of them, the unit reservoirs are measured in.
Is fixing leaks cheaper than new supply?
Almost always, up to a point. The row showing the saving from halving losses is the number to put against a new dam.
Where these figures come from
- UN-Habitat — Urban Indicators Guidelines — density, green space and public space benchmarks
- World Health Organization — Urban green spaces — the 9 m² per person minimum
- ITE — Parking Generation Manual — parking demand rates by land use
- US Census Bureau — Population and housing — the US national statistics agency
Last checked: September 2026. Default per-capita rates are mid-range figures from national statistical agencies and utility reports; every one is an input you should replace with the local figure.