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Residential Water Demand with Peak Multipliers

Estimate average, maximum-day and peak-hour flow rates from population and per-person demand, including the retained 10% allowance and adjustable peak factors.

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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

For 1,000 people at 225 L per person per day, the fixed 10% allowance gives 247,500 L/day average demand. Multipliers of 1.4 and 2.3 give 346,500 L/day maximum-day demand and about 6.589 L/s peak-hour flow.

Average = population × per-person demand × 1.10; maximum day = average × factor₁; peak hour = average × factor₂

Worked example

Enter these known values and leave the other values blank.

Population size
1000
Water flow per person
225 L/day
Maximum-day / average factor
1.4
Peak-hour / average factor
2.3
Average flow including 10% allowance
247500 L/day
Maximum-day flow rate
346500 L/day
Peak-hour flow rate
6.5885 L/s

Assumptions and limitations

  • The model multiplies the entire population demand by 1.10. This fixed 10% allowance is not an extra 0.1 L per person.
  • The starting 225 L/person/day and factors 1.4 and 2.3 reflect the cited residential estimation method. They are editable assumptions, not universal consumption or peak-demand measurements.
  • The imperial starting value is 60 US gal/person/day, which is a separate rounded preset rather than exactly 225 L/person/day. Enter a consistent rate when comparing unit systems.
  • All three outputs are flow rates. A peak-hour rate shown in L/s is the equivalent instantaneous rate; it is not a daily volume squeezed into one second.
  • This estimates population demand under entered factors. Fire flow, pipe hydraulics, land-use mixtures and local design approval are outside this calculation.

Common questions

How do I convert a daily rate to liters per second?

Divide liters per day by 86,400. The selected output unit performs that conversion after the demand multiplier is applied.

References

Volumetric flow rates use exact US or imperial fluid-volume definitions and exact seconds per minute, hour and day.

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