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Water Loss & Leaks · E1

Pool Evaporation Rate Calculator

Estimate how much water your pool loses to evaporation each day, month, and year — and what it costs.

Measure the inputsEvaporation is normal — most pools lose a quarter to half an inch a day in summer.
Read the full resultWarm water plus dry, windy air is the worst combination for evaporation.
Check the boundaryA solar cover cuts evaporation by roughly 90% — the biggest single water saver.

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Live calculation

Evaporation inputs

✓ Checked May 2026

Enter surface area, temps, humidity, wind, and cover.

Change a value. See the result.

Required fields are marked *. Engine validation and warnings remain active.

Enter the known values. Let the engine handle the calculation.

✓ Formula checked↻ Live result○ No account needed

Planning estimate only. Confirm product labels, equipment specifications, qualified-professional advice and local requirements before acting.

The result, explained

Use the Pool Evaporation Rate Calculator result with context.

Estimate how much water your pool loses to evaporation each day, month, and year — and what it costs.

01

The purpose

What does this calculator estimate?

Estimate how much water your pool loses to evaporation each day, month, and year — and what it costs.

02

The tool

What information does it use?

  • Pool surface area: Length × width of the water surface.
  • Air temperature: enter a measured or verified value
  • Water temperature: Warmer water evaporates faster.
  • Humidity: % — drier air evaporates more.
  • Wind speed: Wind sharply increases evaporation.
  • Using a solar cover?: A cover cuts evaporation ~90%.
  • Water rate: $ per gallon.
03

The method

How to use this calculator

  1. Pool surface areaLength × width of the water surface.
  2. Air temperatureEnter the value you can verify.
  3. Water temperatureWarmer water evaporates faster.
  4. Humidity% — drier air evaporates more.
  5. Wind speedWind sharply increases evaporation.
  6. Using a solar cover?A cover cuts evaporation ~90%.
  7. Water rate$ per gallon.
04

The relationship

The formula in plain English

Evaporation rises with the vapor-pressure gap (warm water, dry air) and with wind

Gallons/day = (inches/day ÷ 12) × surface area × 7.48. A cover multiplies evaporation by ~0.1.
05

Worked through

A worked example: 500 sq ft pool losing 0.3 in/day, uncovered

  1. Gallons/day = (0.3 ÷ 12) × 500 × 7.48 = 93.5 gal
  2. Per month ≈ 2,805 gal
  3. Per year ≈ 34,128 gal ≈ $171 at $0.005/gal
Approximate daily evaporation loss by surface area (warm, moderate conditions, uncovered).
Surface area~0.25 in/day~0.375 in/day~0.5 in/day
300 ft²47 gal70 gal94 gal
400 ft²62 gal94 gal125 gal
500 ft²78 gal117 gal156 gal
600 ft²94 gal140 gal187 gal
800 ft²125 gal187 gal249 gal
06

Why it matters

How the result supports the next decision

Evaporation is normal — most pools lose a quarter to half an inch a day in summer.

Warm water plus dry, windy air is the worst combination for evaporation.

07

Good inputs

Improve the estimate before relying on it

  • Evaporation is normal — most pools lose a quarter to half an inch a day in summer.
  • Warm water plus dry, windy air is the worst combination for evaporation.
  • A solar cover cuts evaporation by roughly 90% — the biggest single water saver.
  • Lowering water temperature a couple degrees noticeably slows evaporation.
  • A windbreak around the pool reduces both evaporation and heat loss.
08

The boundary

How to interpret the result

Measurements, equipment specifications, site conditions and local requirements can change the practical result.

The engine reports invalid inputs and safety warnings beside the result. Resolve those messages before using the estimate.

09

Before acting

What should override this estimate?

  • Measured site conditions and current test results
  • Product labels and manufacturer specifications
  • Qualified-professional advice and applicable local codes
10

Common questions

Frequently asked questions

How much water does a pool lose to evaporation?

A typical uncovered pool loses about a quarter to a half inch of water per day, which for a 500-square-foot surface is roughly 80 to 150 gallons daily. The exact rate depends on water temperature, air temperature, humidity, and wind — hot, dry, breezy conditions push it much higher.

What causes pool water to evaporate faster?

Evaporation is driven by the gap between the water's vapor pressure and the air's humidity, amplified by wind. Warm water, dry air, and breeze all widen that gap and speed evaporation. That's why a heated pool on a dry, windy night can lose surprising amounts of water and heat together.

Is it normal to lose half an inch of water a day?

Yes, in warm or windy weather that's completely normal evaporation, not a leak. If you're losing significantly more — say, over an inch a day — or losing water in cool, humid, calm conditions, then a leak becomes more likely and a bucket test is worth doing.

How do I reduce pool evaporation?

A solar or solid cover is by far the most effective step, cutting evaporation by around 90 percent. Beyond that, lowering the water temperature slightly, adding a windbreak, and reducing aeration features like fountains and waterfalls all help slow the loss.

Does evaporation increase water bills?

Yes — every inch that evaporates is water you must replace, and replacing it costs money and adds fresh minerals that raise calcium and TDS over time. In hot climates, evaporation can be the single largest source of pool water loss, which is why covers pay back quickly.

How much water evaporates from a pool per day?

Roughly a quarter to a half inch daily for an uncovered pool — about 80–150 gallons for 500 sq ft.

How do I know if it's evaporation or a leak?

Run a bucket test: if the pool drops faster than a bucket of pool water beside it, you likely have a leak.

Does a cover stop evaporation?

A solar or solid cover stops about 90% of evaporation — the most effective water-saving measure.

Primary sources

Use the result with current guidance.

These official references support safe planning context. Product labels, local requirements and qualified-professional advice take priority over a general calculator estimate.