Why Your Pool Is Losing Water
A pool loses water three ways: evaporation, normal use and leaks. Evaporation takes up to about a quarter inch a day in a Florida summer. Splash-out, backwashing the filter and overflow drains after heavy rain add more. Anything beyond that, especially loss that continues on cool, calm days, points to a leak.
| Cause | What it looks like | Leak? |
|---|---|---|
| Evaporation | Steady, faster on hot, windy, dry days | No |
| Splash-out | Drops after parties, kids or dogs swimming | No |
| Backwashing | Level falls each time you backwash the filter | No |
| Overflow drain | Level resets lower after heavy rain | No |
| Leak | Loss beyond all of the above, every day | Yes |
Normal Water Loss vs a Leak
Up to about a quarter inch a day is normal evaporation for an uncovered pool in summer, and less in cooler months. Wind, low humidity, a heated pool and waterfalls push it higher. Half an inch a day or more is about double that rule of thumb and worth a bucket test.
The number alone can mislead, because a hot, breezy week can push a sound pool past a quarter inch. That's why the side-by-side bucket test below matters more than any rule of thumb: it measures your own pool's evaporation on the same days.
Free 24-Hour Bucket Test Before You Call
Set a bucket of pool water on the first or second step, mark the water line inside the bucket and the pool level on its outside, and wait 24 hours with the auto-fill off, no swimmers and no rain. If the pool drops more than the bucket, the extra loss is likely a leak.
- Fill the pool to its normal level and turn off any auto-fill.
- Fill a bucket with pool water to about 1 inch from the top.
- Set it on the first or second step so it sits about 5–6 inches deep in the pool water.
- Mark the water line inside the bucket and the pool level on the outside.
- Wait 24 hours with no swimmers and no rain.
- If the pool dropped more than the bucket, you likely have a leak.
Test twiceRun it once with the pump on and once with it off. More loss with the pump on points to the return side; more with it off points to the suction side, like the skimmer or main drain.
Leak or Evaporation: Clues to Watch
Compare the pool with something that only evaporates. In a bucket test the bucket loses only to evaporation, so any extra drop in the pool is leakage. Other leak clues: loss that stays the same on cool days, changes with the pump on or off, or stops at the skimmer or light.
| Clue | Evaporation | Likely leak |
|---|---|---|
| Daily loss | Up to about ¼ inch in summer | More than ¼ inch, and the bucket test fails |
| Bucket test | Pool and bucket drop the same | Pool drops more than bucket |
| Cool, calm days | Loss slows down | Loss stays about the same |
| Pump on vs off | No real difference | Loss changes with pump state |
| Where it stops | Keeps dropping slowly | Stops at the skimmer or light |
If the level stops at the skimmer mouth, read about skimmer leak repair. If the loss changes with the pump, pool pressure testing checks each line.
Auto-Fill Valves Can Hide a Leak
An auto-fill or auto-leveler tops the pool up from your water line, so the level looks steady while a leak runs. The clue is a water bill that climbs with no other cause. Turn the auto-fill off a day before a bucket test to see the real loss.
If you're on city or county water, compare your last few bills with the same months last year. A steady rise with no new irrigation or guests is worth a test. Wet ground near the auto-fill line itself can also mean the fill line is leaking, not the pool.
Get Pool Leak Detection When the Test Fails
Call when the pool fails a bucket test, drops more than about a quarter inch a day for several days, or shows wet ground, cracks or air in the returns. A specialist then tests each line and fitting with the water in, so the repair targets the right spot.
See what a leak detection visit involves, how leaks are found and what testing typically costs in Sarasota. Already know where the leak is? Read about pool leak repair options and prices.
Pool failed the bucket test?Call to reach an independent local pool leak specialist. Free referral; the specialist may pay us a fee.
Call (833) 710-2588Pool Water Loss FAQs
Short answers to the questions pool owners ask most when the level keeps dropping: what's normal, how backwashing and rain affect it, and when it's time to test. For anything specific to your pool, call and describe what you're seeing.
Is it normal for a pool to lose half an inch of water a day?
Usually not. Half an inch a day is about double the summer evaporation rule of thumb, so it's worth a bucket test. Wind, very hot days and a running waterfall can push evaporation up, which is why the side-by-side test matters more than the number alone.
Does backwashing lower the pool level?
Yes. Backwashing sends pool water out through the waste line, so the level drops each time you do it. Note the level before and after. If it keeps falling when you're not backwashing, check that the multiport valve isn't leaking to waste.
Why does my pool lose more water in summer?
Heat, sun, wind and low humidity all speed up evaporation, and summer brings more swimming and splash-out. A covered pool loses far less.
Can rain hide a pool leak?
Yes. Heavy rain refills the pool and can mask a slow leak for weeks. Run your bucket test during a dry spell for a clear result.
