Pool bucket test for leak detection on a daylight deck

Pool Water Loss: Evaporation vs Leak

You’re adding water to your pool every other day and wondering if you have a leak or just normal evaporation. The answer matters — a real leak left untreated damages plumbing, lifts pool decks, and runs your water bill up dramatically. Here’s how to tell the difference.

Normal evaporation rate

A typical residential pool loses 1/4″ to 1/2″ per day to evaporation in summer, and slightly less in cooler weather. For a 20,000 gallon pool, that’s 100–300 gallons per week from evaporation alone.

Higher loss factors:

  • Hot, dry, windy climate (desert Southwest).
  • Direct sun exposure with no shade.
  • Heated pool (warmer water evaporates faster).
  • Waterfall or fountain features (water exposed to air more).
  • Heavy bather use with splash-out.

If you’re losing more than 1″ per day for several days in a row with no obvious wind/sun/heater explanation, you might have a leak.

The bucket test (the standard leak detection)

1Fill a 5-gallon bucket with pool water to within 1 inch of the rim. Set it on a pool step so it’s partially submerged.
2Mark the water level inside the bucket AND the water level in the pool (use waterproof tape or a grease pencil).
3Wait 24 hours. Don’t use the pool. Don’t run any features.
4Compare the two marks. The bucket water only evaporates (no leak path). The pool water evaporates AND drains through any leak.

If the pool dropped more than the bucket, you have a leak. The size of the difference tells you the severity.

Pump on vs. pump off test

To narrow down where the leak is:

  1. Mark the water level. Run the pump for 24 hours. Note how much water you lost.
  2. Mark the level again. Shut the pump off for 24 hours. Note how much water you lost.
  • More loss with pump ON = leak is in the return-side plumbing (pressure side).
  • More loss with pump OFF = leak is in the suction-side plumbing (pulls air in when running, pulls water out when not).
  • Equal loss = leak is in the pool shell itself (liner tear, plaster crack, light niche).

Common leak locations

  • Skimmer faceplate (where the skimmer meets the pool wall)
  • Underwater light niche seal
  • Return jet fittings
  • Main drain pot
  • Underground PVC plumbing (hard to find without a professional)

Equipment that minimizes water loss

Pool Season liquid solar cover for reducing evaporation

Pool Season Liquid Solar Cover

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AquaPill solar liquid blanket

AquaPill #73 Solar Liquid Blanket

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Pump lid gasket o-ring

Pump Lid Gasket O-Ring

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If your bucket test confirms a leak you can’t locate, reach out to PST Pool Supplies for guidance on professional leak detection services in your area.

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