Every pool loses some water to evaporation — in the South Bay's warm, breezy climate, that's just physics. But there's a big difference between normal evaporation and a leak that's quietly draining hundreds of gallons and undermining the surrounding soil or equipment pad. The bucket test, used by pool professionals everywhere, settles the question in 24 hours with nothing more than a bucket and a marker.
How much water loss per day is normal?
The commonly cited guideline is up to about a quarter inch per day from evaporation under normal conditions — more on hot, windy, low-humidity days, less when it's cool and still. Heated spas lose more. If you're losing half an inch or more daily, or you're adding water every couple of days just to keep the level up, that's beyond evaporation and worth investigating. Keep in mind that splash-out from heavy use and backwashing also lower the level; the bucket test below controls for all of that.
How do I do the 24-hour bucket test, step by step?
You'll need a 5-gallon bucket, a waterproof marker or tape, and 24 hours of normal weather (no rain, no extreme wind event). Step 1: Fill the bucket about three-quarters full with pool water and place it on a pool step so the bucket's water level roughly matches the pool's. Step 2: Mark the water level inside the bucket and the pool's level on the skimmer or tile line. Step 3: Run the pump normally for 24 hours — don't add water, don't backwash. Step 4: Compare. If the pool dropped significantly more than the bucket, water is leaving the pool somewhere other than evaporation — you have a leak. If both dropped equally, it's evaporation. Repeat once to confirm before drawing conclusions.
If the pool loses more water with the pump running, what does that mean?
This is the most informative variation of the test. Run the 24-hour test with the pump on, then repeat with the pump off (or vice versa). If water loss is clearly worse with the pump running, the leak is almost certainly on the pressure side — the return lines, fittings, or equipment after the pump, where water is pushed out under pressure. If loss is the same or worse with the pump off, suspect the structure or suction side: the shell, skimmer, main drain, or suction plumbing. That single comparison tells a leak specialist where to start looking.
My spa loses water faster than my pool — is that normal?
In a combo pool-spa setup, the spa normally sits slightly higher and spills over into the pool. If the spa level drops while the pool stays steady, check the spillover and the check valve that prevents spa water from draining back to the pool when the pump is off — a failed check valve lets the spa slowly equalize downward overnight, which looks exactly like a leak. Also check for a stuck actuator valve sending spa water to the pool returns. If the equipment checks out and the spa still drops, the spa shell, jets, or dedicated plumbing may be leaking.
Common leak spots to check first
Before calling anyone, do a visual sweep: the skimmer throat (gaps in the sealant are a top leak source), return fittings, pool light niches, tile-line cracks, and the equipment pad (wet spots under the pump, filter, or heater indicate equipment-side leaks). Check the backwash line too — a multiport valve stuck partially in backwash position silently sends pool water to waste. Look for soggy soil or sinkholes around the pool shell, and listen near the equipment for hissing when the pump runs. Finding an obvious culprit here saves everyone time — but if everything looks fine and the bucket test says leak, the problem is underground or structural, and that's a job for instruments.
What to do next
If the bucket test confirms a leak, note whether it's worse pump-on or pump-off — that detail focuses the search immediately. Pool and spa leak detection in Hawthorne uses pressure testing, dye testing, and acoustic listening to find the exact failure without draining the pool or digging blindly. Call +1 424-544-0197 — open 24 hours.
Related service: Pool & Spa Leak Detection in Alhambra, CA