Every pool loses water. The question is whether it's evaporation (normal) or a leak (not normal). In Florida summer, a healthy pool can lose a quarter inch per day to evaporation alone. That's why the eye test — “my pool is low” — is never enough. You need a method.
Step 1: the bucket test (free, 24 hours)
- Set a 5-gallon bucket on the first or second step of the pool. Fill it with pool water to a level matching the pool level exactly.
- Mark both the pool level and the bucket level with tape.
- Leave the pool running normally for 24 hours. Don't swim.
- Compare the two drops. Pool and bucket drop by the same amount → evaporation, no leak. Pool drops noticeably more than the bucket → you have a leak.
Run the test twice: once with the pump running and once with it off. If the leak only appears with the pump running, it's on the pressure side (return lines, filter, heater, cleaner line). If it only appears with the pump off, it's on the suction side or in the shell itself. If it leaks both ways, it's in the shell or at a fitting above the water line.
Step 2: narrow by category
- Shell / surface leak— cracks in plaster, gaps around tiles, failing light niche, separation at skimmer throat. Check visually for stains, soft spots, or settled deck near the suspected spot.
- Plumbing leak— underground pipe, equipment-pad fitting, or equipment body (pump seal, filter clamp, heater manifold). See the pressure-testing guide for the next step.
- Equipment-area leak— drip around the pump volute, under the filter, at a union. Often the fastest to find because it's all above ground.
Dye testing: the field technique every tech should know
A small bottle of pool-grade test dye (or even food coloring) finds shell leaks that otherwise require divers. Turn the pump off and let the water fully settle. Release dye gently near a suspected fault line — around the light niche, along a plaster crack, at the skimmer throat. If water is escaping there, the dye plume will be visibly sucked into the defect. No plume, no leak at that spot.
What rate of loss tells you
| Daily loss (after subtracting evap) | Likely cause |
|---|---|
| < 1/8" | Small shell leak, fitting seepage, or you're still seeing evaporation differences. |
| 1/4" to 1/2" | Confirmed leak. Plumbing or skimmer throat is most common. |
| 1" or more | Significant leak. Usually a broken main-drain line, failed return, or a split at an equipment-pad fitting. Call a pro — fast water loss can cause deck settling and plaster cracking. |
When to call a leak-detection specialist
If the bucket test confirms a leak and you can't locate it above ground, it's worth the specialist's fee before you start cutting concrete. Professional leak detection uses acoustic sensors, dye kits, thermal imaging, and tracer gas to find underground leaks to within an inch. The cost of a bad guess (pulling up the wrong section of deck) is several times the cost of the detection call.