Heat, sun and dry wind can take a lot of water out of a pool in a single afternoon. On a hot week, a normal drop and a leak can look about the same from the deck. That’s why the first question with any pool that keeps dropping is the same: is it a leak or just evaporation?
You can answer most of that yourself with a bucket and a marker.
Why there’s no single “normal” number
Evaporation depends on heat, wind, shade and humidity, so the same pool loses very different amounts in July and January. A shaded pool in Encino and a pool in full sun a few miles west can lose very different amounts in the same week. A rule of thumb from the internet won’t tell you much about your pool. A bucket test will.
How to run a bucket test
A bucket of pool water sitting on the step gets the same sun and wind as the pool. Both lose water to evaporation. Only the pool can lose it to a leak.
- Turn off the auto-fill and don’t add water during the test.
- Set a bucket on the first or second step.
- Fill it until the water inside matches the pool level outside.
- Mark the water line inside the bucket.
- Mark the pool level on the outside of the bucket.
- Run the pump on its normal schedule for 24 hours, with nobody swimming.
- Measure how far each level dropped.
- Reset the marks and repeat for 24 hours with the pump off.
Rain spoils the result.
If it rains during either 24-hour run, start over.
Reading the result
If the pool and the bucket dropped about the same, it’s evaporation. If the pool dropped noticeably more, the difference is leaving some other way.
What the pump-on and pump-off runs tell you
- More loss with the pump running often points to the return lines, which are under pressure while the pump runs.
- More loss with the pump off tends to point to the suction side.
- About the same both ways makes the shell, the tile line or a fitting in the wall the likelier suspect. Water that drops and then holds at the skimmer or the light is often leaking at that height.
These are rules of thumb, not a diagnosis, but they’re a useful first clue about whether the problem is in the structure or the plumbing.
A note on spas
One pattern isn’t a leak at all. A raised spa that drops while the pool rises is usually water passing back through a leaking valve or a damaged spillover. It’s worth fixing, but the water hasn’t left your yard.
Pool losing more than the bucket? See pool leak detection or request service.
