Daily Water Consumption Calculator

This calculator starts from the most basic water supply design number — how many people the system serves — and builds up to the three figures a water supply engineer actually needs: average daily demand, gross demand after accounting for distribution losses, and peak hour demand.

Average daily demand is simply population multiplied by per capita consumption. A town of 50,000 people at 135 litres per capita per day (LPCD) consumes about 6,750 m³ (6.75 MLD) of water on an average day.

Gross demand (with losses) scales that figure up to account for unaccounted-for water (UFW) — leakage, metering inaccuracies, and unbilled but legitimate use such as firefighting tests or flushing. A treatment plant has to produce the gross figure, not just the consumption figure, because water lost in the network never reaches a consumer's tap.

Peak hour demand recognises that consumption isn't flat across the day — mornings and evenings see sharp spikes as households cook, bathe and clean. Distribution pipes, pumps and elevated service reservoirs are sized on this peak figure, not the daily average, because that's the flow the network must be able to deliver at the busiest moment without a pressure drop.

The average or gross demand from this tool is a natural design flow (Q) to carry into the WTP Pro Cal toolkit — feed it into the Sedimentation Tank, Filtration Rate, and Coagulant Dosage tabs there to size the rest of the treatment train.

1. Sizing the treatment plant on consumption demand instead of gross demand. Leaving out UFW/losses under-sizes the plant — it has to treat and pump more water than residents actually consume, since a meaningful share never reaches the tap.
2. Using a single national-average LPCD figure regardless of city size or climate. Per capita demand rises with city size, income level, and climate (hotter regions consume more); CPHEEO gives ranges, not a single fixed number, for exactly this reason.
3. Designing pipes and pumps on average daily demand. The distribution network must deliver the peak hour demand without a pressure drop — sizing on the daily average alone leaves the system unable to cope during the morning and evening consumption spikes.
4. Forgetting industrial, commercial or institutional demand. This calculator covers domestic per capita demand only — bulk consumers (industry, hospitals, large commercial buildings) need to be added separately, often as a lump-sum or metered addition to total demand.
5. Never revisiting the design population. Demand projections are usually based on a 20–30 year design horizon population, not today's population — using today's number alone under-sizes infrastructure meant to serve future growth.