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Calcimator

Water Demand Forecasting Calculator

Forecast future water demand based on population growth, per capita usage, and peak factors. Estimates required storage capacity.

Inputs

%
years
gpd

AWWA M1: residential 80–100 gpd; total system 100–150 gpd; arid western US up to 200 gpd

AWWA M1: small system PHF 3.0–4.0; medium 2.0–3.0; large 1.5–2.5

Results

Average Daily Demand

7.43 MGD

Max Daily Demand

11.15 MGD

Required Storage

5.14 MG

Future Population74,297
Peak Hourly Demand14.86 MGD
How to Use This Calculator
  1. Enter current population, annual growth rate (%), and per-capita water demand (gpd).
  2. Set projection period in years.
  3. Review projected demand at 10, 20, and 30 years for infrastructure planning.

How the result changes with Current Population

Current PopulationAverage Daily DemandMax Daily DemandRequired Storage
1,000,090148.61 MGD222.91 MGD93.38 MG
3,500,065520.09 MGD780.14 MGD325.56 MG
6,500,035965.87 MGD1,448.81 MGD604.17 MG
9,000,0101,337.35 MGD2,006.03 MGD836.35 MG

What each input means

Current Population
Current population served by the water system. Use census data or utility service records.
Annual Growth Rate
Projected annual population growth rate. US average is ~0.5%; fast-growing areas may be 2-5%.
Planning Horizon
Design period for the water system. Typical planning horizons are 20-30 years.
Per Capita Demand
Average gallons per person per day per AWWA M1 manual. US average ≈ 80–100 gpd residential; total system demand (including commercial/industrial) ≈ 100–150 gpd. Western arid cities can reach 150–200 gpd.
Peak Hour Factor
Ratio of peak hourly demand to average daily demand per AWWA M1. Small systems (<1 MGD): PHF 3.0–4.0; medium (1–10 MGD): 2.0–3.0; large (>10 MGD): 1.5–2.5. Used to size distribution mains and storage.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Current Population = 50000, Annual Growth Rate = 2, Planning Horizon = 20, Per Capita Demand = 100 = 5 input(s) provided
  2. Calculate Average Daily Demand
    Average Daily Demand
    7.43 = 7.43
  3. Calculate Max Daily Demand
    Max Daily Demand
    11.145 = 11.145
  4. Calculate Required Storage
    Required Storage
    5.14 = 5.14
  5. Calculate Future Population
    Future Population
    74297 = 74297
  6. Calculate Peak Hourly Demand
    Peak Hourly Demand
    14.859 = 14.859

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