Pool, Spa & Water Treatment Chemistry worked example

Evaporation Water Loss with water surface area of 260 ft2: a worked example

This worked example runs the evaporation water loss numbers for a tougher week than the baseline: water surface area of 260 ft2 instead of the typical 512 ft2. Estimate evaporation loss from surface area, evaporation depth, and gallon conversion.

The inputs for this scenario

  • Water surface area: 260 ft2 (the input this scenario stresses; the baseline uses 512)
  • Daily evaporation depth: 0.25 in / day (held at the documented default)
  • Gallons per square foot-inch: 0.62 gal / ft2-in (held at the documented default)
  • Exposure adjustment factor: 1 x (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Evaporation loss = surface area x evaporation depth x 0.623 x exposure adjustment.
  • Evaporation water loss works out to 40.49 gal / day at these inputs, and this is the headline figure for the scenario.
  • Base product works out to 40.49 value at these inputs.
  • Multiplier works out to 1 x at these inputs.
  • Factor A x B works out to 65 value at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where water surface area sits at 512 ft2 and the headline result is 79.74 gal / day, this scenario comes in 49.22% below the baseline at 40.49 gal / day.
  • Use it when diagnosing high make-up water use or evaluating the water and heat savings of installing a pool cover. A result at this level usually justifies acting on the stressed input before touching anything else, because every other figure in the table is downstream of it.

Results at a glance

  • Evaporation water loss: 40.49 gal / day (headline result)
  • Base product: 40.49 value
  • Multiplier: 1 x
  • Factor A x B: 65 value

Run it with your numbers

  • To rerun this with your own numbers, open the live Evaporation Water Loss calculator, set water surface area to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.