Is your pool losing water? How to tell a leak from evaporation

Pool Sense · Updated September 3, 2026 · Written for HOA boards, property managers, and facility directors in Georgia

What evaporation actually takes

A Georgia summer evaporates roughly a quarter inch of water from a pool surface each day. Hot, dry, windy days take more; humid, overcast, or rainy days take less; a pool cover cuts it by two-thirds; water features and heated water raise it. On a typical July day, a quarter inch is a fair working number.

To turn inches into gallons, multiply the pool's surface area in square feet by the inches lost and by 0.623. A 20-by-40 pool, 800 square feet, losing a quarter inch is about 125 gallons a day. A large HOA pool at 2,500 square feet is closer to 390 gallons. Splash-out from a busy weekend and the water sent down the drain in a backwash add to it, and a heavy rain adds water back.

The bucket test

The classic way to separate evaporation from a leak takes a bucket and two days.

1. Fill a bucket most of the way and set it on a pool step so the bucket sits in the water without floating. Turn the autofill off.
2. Mark the water level inside the bucket and the pool's water level on the outside of the bucket, at the same moment.
3. Run the pump on its normal schedule for 24 to 48 hours. No swimming, no backwash.
4. Compare. The water in the bucket and the water in the pool evaporate at the same rate. If the pool dropped more than the bucket, the difference is a leak.
5. Repeat with the pump off. If the loss is larger with the pump running, the leak is on the pressure side of the plumbing. If it is larger with the pump off, it is on the suction side or in the shell.

The bucket test works, but it needs the autofill off, no swimmers, and two days of attention. That is the problem for a commercial pool.

Why an autofill hides a leak

Most commercial pools have an automatic fill: a float valve or a level sensor opens a water line whenever the level drops. It keeps the skimmers working and the pump from running dry, which is good. It also means the level never visibly drops, so no one ever runs a bucket test. A leak of 300 gallons a day is invisible at the pool and shows up months later as a water bill that is a few hundred dollars higher than the same month last year. By then a season's worth of treated, heated water has gone into the ground, along with the chemicals in it.

Where commercial pools leak

In rough order of how often we find them:

• Skimmers. The joint between the skimmer body and the pool shell separates as the deck and the shell move differently. The throat cracks. This is the most common leak on a pool more than fifteen years old.
• Return fittings and light niches. The conduit behind a light and the fittings where returns enter the shell both leak at the seal.
• The main drain sump and the hydrostatic relief valve in it.
• Underground plumbing, especially on older pools with original PVC or, on very old pools, galvanized pipe. A pressure-side leak shows up as a wet spot in the lawn or a settling deck.
• The equipment pad. Pump seals, filter tank seams, valve stems, and unions. These are the easiest to find and are usually spotted on a routine visit.
• The shell. Plaster cracks leak less often than people expect. Structural cracks in gunite do, but they are visible.

How we find it without a bucket

On pools we service, the autofill is metered. The controller sees the fill valve open and close, and PoolSense Intelligence turns that into gallons added each day. Then it compares the water added against what that day's weather should have required, using the pool's surface area, the day's temperature, sun, humidity, and wind, the rain that fell, and any backwash we ran. When the water added runs well above the expectation, and keeps running above it day after day, the leak-likelihood reading climbs. One hot, windy day does not trigger it; a week of doubled fills does.

A high reading gets a diagnostic visit: dye testing at the skimmers, returns, and light niches, pressure testing the plumbing runs, and isolating sections. We quote the diagnostic and then the repair. Most leaks we find are at a skimmer or a fitting and are fixed in a day.

When to call

• The water bill is up and nothing else changed.
• The autofill runs every day, or you can hear it running at night.
• There is a wet or unusually green spot in the lawn near the pool or along the plumbing route.
• The deck is settling or cracking near the skimmers.
• The pool loses more than a quarter inch a day with no swimmers and no backwash.
• The chemistry will not hold: constantly adding stabilizer and calcium is a sign the pool is being diluted by makeup water.

A leak ignored for a season costs the water, the chemicals to treat the makeup water, the heat if the pool is heated, and the risk of undermining the deck or the shell. It does not fix itself. Ask for an assessment and we will tell you what the data says.