Water Demand For Population Calculator

Work out water demand for population instantly with clear inputs, formula shown and shareable results.

About Water Demand For Population Calculator

Domestic demand is population times per capita consumption. Institutional, commercial and industrial demand is added as a share, and the whole is grossed up for unaccounted-for water — leakage, meter error and unbilled use — which commonly runs 15-30% in developing distribution networks.

Formulas

Water demand

Domestic (m3/d) = population x per capita demand / 1000

Gross demand

Gross = domestic x (1 + non-domestic share) / (1 - unaccounted-for water)

Worked example

With the default values below, Water Demand For Population Calculator returns Gross Daily Water Demand of 9,878.05. Change any input above and every figure here is recalculated in your browser.

Inputs used

Population Servedminimum 0: 50,000
Per Capita Demandminimum 0 litres/person/day: 135 litres/person/day
Non-Domestic And Institutional Shareaccepts 0–100 %: 20 %
Unaccounted-For Wateraccepts 0–60 %: 18 %

Results

Gross Daily Water Demand: 9,878.05
Domestic Demand: 6,750.00
Annual Demand: 3.6055
Average Design Flow: 114.329

Step by step

1Values used
2Water demand
3Gross demand
4Gross Daily Water Demand= 9,878.05
5Domestic Demand= 6,750.00
6Annual Demand= 3.6055
7Average Design Flow= 114.329

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

What per capita figure should be used?

Design standards commonly specify 135 litres per person per day for piped sewered communities and 70-100 where sewerage is absent. Metered actual consumption is a better basis where data exists.

Why does unaccounted-for water matter so much?

It sizes every asset upstream of the leak. Reducing it from 30% to 15% cuts required source, treatment and pumping capacity by nearly 18%, usually far cheaper than building new capacity.