Pool, Spa & Water Treatment Chemistry worked example

Make-up Water Rate with total make-up water added of 2,100 gal: a worked example

Suppose total make-up water added falls to 2,100 gal. This page works the full calculation at that level so you can see exactly which result moves and by how much. Estimate make-up water need from backwash, splash-out, evaporation, leaks, and operating days.

The inputs for this scenario

  • Total make-up water added: 2,100 gal (the input this scenario stresses; the baseline uses 4,200)
  • Reporting period length: 30 days (held at the documented default)
  • Meter calibration factor: 1 x (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Make-up water rate = total make-up volume / operating days x factor.
  • Ratio works out to 70 gal / day at these inputs, and this is the headline figure for the scenario.
  • Raw ratio works out to 70 value at these inputs.
  • Meter factor works out to 1 x at these inputs.
  • Operating days works out to 30 value at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where total make-up water added sits at 4,200 gal and the headline result is 140 gal / day, this scenario comes in 50% below the baseline at 70 gal / day.
  • It computes the average daily volume of fresh water added to a pool or spa over a reporting period, adjusted for meter bias. When the numbers land here, the stressed input is the lever to work; the walkthrough above shows exactly how much each output recovers as it climbs back toward the baseline.

Results at a glance

  • Ratio: 70 gal / day (headline result)
  • Raw ratio: 70 value
  • Meter factor: 1 x
  • Operating days: 30 value

Run it with your numbers

  • To rerun this with your own numbers, open the live Make-up Water Rate calculator, set total make-up water added to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.