Estimate how much water your pool loses to evaporation daily. Compare to actual water loss to detect potential leaks.
For irregular shapes, estimate the average length and width.
Measure over 24 hours with pump off
Adjusts expected evaporation rate
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Your water loss appears to be within normal evaporation range.
Understanding how much water your pool loses to evaporation is essential for detecting leaks, managing water costs, and maintaining proper chemistry. This calculator helps you estimate expected evaporation and compare it to actual water loss.
Pool water evaporates when water molecules gain enough energy to escape the surface and become water vapor. Several factors influence the evaporation rate:
Typical pool evaporation rates vary by climate and conditions:
For a typical 400 sq ft pool, 1/4" of water loss equals approximately 62 gallons.
The bucket test is the most reliable way to measure evaporation and detect leaks:
If both dropped equally, you have normal evaporation. If the pool dropped more than the bucket, you likely have a leak.
To convert water level drop to gallons lost:
Gallons Lost = (Drop in inches ÷ 12) × 7.48 × Surface Area (sq ft)
For example, a 20×40 ft pool (800 sq ft) that drops 0.25 inches in one day:
Gallons = (0.25 ÷ 12) × 7.48 × 800 = 125 gallons per day
Pool covers are the most effective way to reduce evaporation:
Fences, hedges, or screen enclosures reduce wind exposure and can cut evaporation by 20-40%.
Fountains, waterfalls, and spray features increase evaporation significantly. Run them only when enjoying the pool.
Warmer water evaporates faster. If heating your pool, lower temperatures by a few degrees to reduce evaporation.
Normal evaporation ranges from 1/8" to 1/2" per day depending on climate and conditions. In hot, dry, windy weather, losses up to 3/4" per day are possible. For a typical 15×30 ft pool, this equals 30-120 gallons per day.
Perform the bucket test: place a bucket of pool water on a step and mark both water levels. After 24 hours, if the pool dropped more than the bucket, you likely have a leak. If they dropped equally, it's evaporation.
A typical uncovered pool loses 1-3 inches of water per week to evaporation in normal conditions. This can equal 150-500+ gallons per week for an average residential pool.
Yes, significantly. A solar bubble cover reduces evaporation by 70-90%. A solid safety cover reduces it by 95% or more. Even liquid solar covers provide 30-50% reduction with no visible barrier.
Wind removes the layer of humid air just above the pool surface, allowing more water molecules to escape. Windy conditions can double or triple the normal evaporation rate.
Slightly. Water movement and circulation increase surface agitation, which can increase evaporation by 10-20%. However, this is far outweighed by the benefits of proper filtration.
At typical water rates of $0.005-$0.015 per gallon, replacing 100 gallons per day costs $0.50-$1.50 daily, or $180-$550 per year. Water costs vary significantly by location.
Yes. Warmer water evaporates faster. A heated pool (85°F+) can lose 50-100% more water to evaporation than an unheated pool at ambient temperature.
Saltwater pools evaporate at nearly the same rate as freshwater pools. The salt concentration in pools is too low (3,000-4,000 ppm) to significantly affect evaporation rate.
Suspect a leak if: water loss exceeds 1/2" per day in moderate weather, the pool loses water faster than a bucket test, you see wet spots near equipment, or the autofill runs constantly.
Here's what to expect in monthly water loss for a typical 400 sq ft pool:
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