Every pool loses some water to evaporation, especially in Southern California heat, so a dropping water level does not automatically mean a leak. But it might. The difference matters: evaporation is free and normal, while a leak wastes water around the clock and can undermine decking, equipment, and the pool shell itself. Fortunately, there is a simple test that settles the question in about twenty-four hours.
Last updated: October 13, 2026
How much water loss in a pool is normal?
Some evaporation is always happening, and the rate varies with heat, wind, humidity, and how much the pool is used. Splash-out, backwashing the filter, and drips at the equipment pad can also drop the level without any structural leak. As a rule of thumb, if you are refilling noticeably more often than usual for the season, or the level drops visibly day after day, it is worth testing rather than assuming it is the weather. Do not rely on memory; measure. Mark the level and check it at the same time each day for a few days to establish what is actually happening.
How do you do a bucket test for a pool leak?
The bucket test isolates evaporation from leaking with elegant simplicity. Here is how to run it properly:
1. Fill a bucket with pool water and set it on a pool step, so the water level inside the bucket roughly matches the pool's level.
2. Mark the water level inside the bucket and the pool's level on the tile line, painter's tape works well for both.
3. Turn the pump off for this first test. (Plumbing leaks often only show with the system running, so a second test with the pump on can come later, but start simple.)
4. Wait twenty-four hours without swimming, splashing, or backwashing.
5. Compare the two marks. If the pool dropped significantly more than the bucket, water is leaving somewhere other than evaporation, you likely have a leak. If both dropped by about the same amount, it is evaporation.
If the first test is inconclusive, repeat it with the pump running: a leak that only appears with the system on points to the plumbing or equipment rather than the shell, useful information for whatever comes next.
What is the most common cause of pool leaks?
- Skimmer and return fittings, the seals where fittings meet the shell are the single most frequent leak point.
- Underground plumbing, cracked or separated lines serving the skimmer, returns, main drain, or cleaner line.
- Light niches and conduit, water migrates through light conduits more often than owners expect.
- Structural cracks, in the shell, coping, or tile line, especially where ground movement has occurred.
- The equipment pad, pump seals, filter connections, and heater unions can drip steadily and are easy to overlook because they are out of sight behind equipment.
Does a pool leak get worse over time?
Almost always. A leaking fitting rarely seals itself, and water escaping under pressure gradually erodes the surrounding soil or backfill, which can open the leak further and, in some cases, cause decking or coping to settle and crack. Meanwhile the autofill (if you have one) masks the loss by topping the pool up constantly, so the water bill climbs while the visible level looks fine. The pattern is consistent: the longer a pool leak runs, the more water it wastes and the more collateral repair it creates. Early detection is the cheap version of this story.
When should I call a professional for a pool leak?
Call when the bucket test points to a leak, or when you can see the level dropping but cannot find where it is going. Professional pool leak detection goes well beyond the bucket: pressure testing isolates each plumbing line individually to identify the leaking one, dye testing traces cracks and fitting leaks with the pump off, and electro-acoustic listening pinpoints underground pipe leaks without digging up the deck. The sooner a leak is located, the less water it wastes, and the less collateral damage it does to the surrounding structure.
If your Alhambra pool is losing water and the bucket test says it is more than evaporation, our pool and spa leak detection service will find exactly where it is going. Call +1 626-898-6221, we are open 24 hours.
Related service: Pool and Spa Leak Detection in Alhambra, CA