Water Demand Calculator Formula
Understand the math behind the water demand calculator. Each variable explained with a worked example.
Formulas Used
Average Daily Demand
avg_daily = population * per_capita / 1000Average Daily Demand
avg_daily_mld = population * per_capita / 1e6Peak Day Demand
peak_daily = population * per_capita / 1000 * peak_factorPeak Day Flow Rate
peak_lps = population * per_capita * peak_factor / (24 * 3600)Variables
| Variable | Description | Default |
|---|---|---|
population | Population Served | 10000 |
per_capita | Per Capita Demand(L/person/day) | 200 |
peak_factor | Peak Day Factor | 1.5 |
How It Works
Municipal Water Demand Estimation
Water demand planning starts with population and per-capita consumption estimates.
Formulas
Average daily demand = Population x Per capita consumption
Peak day demand = Average x Peak day factor
Per-capita consumption includes domestic, commercial, industrial, and losses (unaccounted-for water). Peak factors account for seasonal and daily variation.
Worked Example
A town of 10,000 people with 200 L/person/day consumption and 1.5 peak factor.
- 01Average daily = 10,000 x 200 = 2,000,000 L/day = 2000 m^3/day = 2.0 MLD
- 02Peak daily = 2000 x 1.5 = 3000 m^3/day
- 03Peak flow = 10000 x 200 x 1.5 / 86400 = 34.7 L/s
Frequently Asked Questions
What is typical per-capita water demand?
Rural communities: 40-100 L/person/day. Small towns: 100-150. Medium cities: 150-250. Large metro areas: 200-400. These include all uses: domestic, commercial, industrial, and system losses (often 15-30%).
What peak factors are standard?
Peak day factor: 1.3-1.8 times average day. Peak hour factor: 2.0-3.5 times average day. These factors size the treatment plant (peak day) and distribution mains (peak hour).
Should I account for population growth?
Yes. Water infrastructure has a design life of 20-50 years. Project the population to the design horizon year using growth rates and plan capacity accordingly.
Ready to run the numbers?
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