Water Demand Calculator — Municipal Water Supply Design
Enter design population, per capita consumption, peak factors, and non-revenue water losses to calculate average daily demand, peak day demand, peak hour flow rate, and total supply required — the core outputs for sizing water supply infrastructure.
L/person/day
%
Peak day demand ÷ (1 − NRW) = 16,875 m³/day total abstraction needed
- 1
Average daily demand (ADD)
50,000 × 150 ÷ 1 000 000 = 7.5Population × per capita demand, converted from L/day to million litres/day. - 2
Peak day demand (PDD)
7.5 × 1.8 = 13.5 - 3
Design supply = PDD ÷ (1 − NRW/100)
13.5 ÷ (1 − 20 ÷ 100) = 16.88
How does this calculator work?
Average daily demand (ADD) = population × lpcd ÷ 1 000 (in m³/day). Multiply by the peak day factor (≈1.5–2) to get Peak Day Demand; divide by (1 − NRW/100) to account for system losses. A city of 50 000 people using 150 L/person/day needs about 7.5 MLD average and roughly 14.4 MLD design supply at 20% NRW and a peak factor of 1.8.
Formula
How this is calculated
Municipal water supply systems must be sized not for average demand but for the worst-case peaks that occur during the day and across seasons. The Average Daily Demand (ADD) is simply population multiplied by the per capita demand (litres per person per day, or lpcd). The Peak Day Demand (PDD) multiplies ADD by the peak day factor — the ratio of the highest daily demand (often on a hot summer day) to the average, typically 1.5–2.0. This governs the sizing of storage reservoirs and treatment capacity.
The peak hour factor translates ADD into the maximum instantaneous flow rate during the busiest hour of the day (early morning and evening peaks). Divided by 24 hours, it gives the peak hourly flow in m³/h or L/s — the design point for distribution mains, pumps, and booster stations.
Non-revenue water (NRW) accounts for water that is produced and treated but does not reach paying consumers: physical losses through pipe leaks, meter under-registration, and unauthorised connections. If 20% of water is lost, the system must produce PDD / 0.80 to actually deliver PDD to customers. Well-managed urban systems in high-income countries target NRW below 15%; many developing-country systems exceed 40–50%. All per capita figures and peak factors in this calculator are editable estimates typical for urban water utilities as of 2024 — verify against local surveys and national standards.
Frequently asked questions
The Average Daily Demand (ADD) is the mean daily water consumption over a year. The Peak Day Demand (PDD) is the highest single-day demand, which can be 1.5–2.5 times the average due to seasonal variation, temperature, and population behaviour. Storage tanks and treatment plants are typically designed for PDD; distribution pipelines are sized for peak hour flow.
Non-revenue water (NRW) is the gap between water entering the distribution system and water that generates revenue. Physical losses (real leakage from pipes and joints) are the largest component. NRW of 30% means a utility must abstract, treat, and pump 30% more water than customers actually use — increasing energy costs, source stress, and capital requirements. Reducing NRW is often the cheapest way to expand effective supply.
Per capita demand varies widely: WHO minimum for survival is 15–20 L/person/day; basic urban service is 50–100 L/day; typical developing-country urban demand is 100–200 L/day; high-income country averages range from 200–500 L/day including all domestic, commercial, and industrial uses. Use local metered data where available; otherwise use national planning standards as a starting point.
Also known as
TG we-Calculate Editorial Team. (2026). Water Demand Calculator — Municipal Water Supply Design [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/water-demand-calculator
TG we-Calculate Editorial Team. "Water Demand Calculator — Municipal Water Supply Design." TG we-Calculate. 2026. https://we-calculate.com/calculator/water-demand-calculator.
TG we-Calculate Editorial Team, "Water Demand Calculator — Municipal Water Supply Design," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/water-demand-calculator
@misc{wecalculate_water_demand_calculator, title = {Water Demand Calculator — Municipal Water Supply Design}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/water-demand-calculator}}, year = {2026}, note = {TG we-Calculate} }
Did this calculator help you?