Pool & pond evaporation calculator
Evaporation depends on surface area, not volume. A typical outdoor pool loses about ¼ inch (6 mm) a day in summer.
How it works
litres per day = surface area (m²) × level drop (mm) — 1 mm over 1 m² is exactly 1 litre. In US units, gallons = area (ft²) × drop (in) ÷ 12 × 7.48. A 32 × 16 ft pool losing ¼ in a day loses 512 × 0.25 ÷ 12 × 7.48 = 80 gallons a day, about 560 a week.
Evaporation or a leak? The bucket test
Put a bucket on a pool step, fill it to the pool’s level and mark both water lines. After 24 hours with the pump on its normal schedule, compare: if the pool dropped noticeably more than the bucket, the extra is a leak. Repeat with the pump off to find out whether the leak is in the plumbing.
A pool cover cuts evaporation dramatically and saves heat, chemicals and water. Waterfalls, fountains and wind increase it.
Questions
How much water does a pool lose to evaporation?
About ¼ in (6 mm) a day in warm weather — roughly 0.5 to 2 in per week depending on heat, humidity and wind.
Do ponds evaporate faster than pools?
Per square foot, similar — but waterfalls and streams add a lot of extra surface and spray. A pond with a waterfall can lose 1 in or more a week more than a still pond.