Overnight water loss happens when the pump is off, which rules out pressure-side plumbing and points directly to the pool shell, skimmer, light, or a gravity-draining line.
Call (954) 290-5177 for a Free Estimate →A pool that drops overnight while the pump is off is almost always leaking from the structure, a crack in the shell, a leaking skimmer, a pool light conduit, or a return fitting that allows water to drain by gravity when the system is not pressurized. Evaporation does not explain overnight drops because evaporation slows significantly at night when temperatures fall and the sun is absent. Where the pool stabilizes in the morning tells you exactly where the leak is.
When the pump is off, the plumbing system is not pressurized. Return lines are not pushing water. Suction lines are not pulling. The only thing moving water out of the pool overnight is gravity, and gravity only works on leaks that are at or below the waterline.
Evaporation still happens at night, but at a fraction of the daytime rate. Air temperatures drop, humidity often rises in South Florida, and there is no solar energy driving surface evaporation. A drop of more than a fraction of an inch overnight is not evaporation. It is water physically escaping through a leak path.
One of the most useful pieces of information in a leak detection job is exactly where the pool stabilizes overnight. The level where it stops dropping tells you where the leak is located.
The skimmer body has separated from the pool shell or cracked at the throat. This is one of the most common overnight leak sources on South Florida pools.
The light niche, conduit seal, or surrounding shell is leaking. The pool drains down to the light level and stops when the leak point is above the waterline.
A return fitting, gasket, or the pipe behind it is allowing water to back-drain overnight when the pump is not maintaining pressure in the line.
A crack in the shell at that depth is allowing water to seep out by gravity. The pool stabilizes when the waterline drops below the crack.
If the pool never stabilizes and keeps losing water, the leak is in the main drain, underground plumbing, or a crack at the deep end floor below the lowest possible stabilization point.
Consistent overnight loss of the same amount suggests a single steady leak source, not evaporation, which varies with weather.
Before you call, mark the water level at the skimmer or on the pool wall at bedtime. Turn off the autofill. Check the level in the morning before turning anything on. Write down how many inches it dropped and exactly where it stopped. That information, especially where it stopped, helps us start in the right place when we arrive.
When a homeowner tells me the pool drops overnight but is fine during the day when the pump runs, that is a very specific pattern. The pump running actually masks the overnight leak by replacing what the structural leak is draining, or the pressure in the return lines prevents back-drainage through the fittings. Either way, overnight loss with pump off tells me structural first, plumbing second.
The single most useful thing a homeowner can tell me before I arrive is where the water stopped. If it stopped right at the skimmer, I am looking at the skimmer first. If it stopped at the light, I am going straight to the light conduit. That one detail saves 30 minutes of testing.
Free tools from Leak Business Academy
Use the Leak Analyzer to score your symptoms, the Evaporation Calculator to check if your loss is normal, and download the free beginner guide to understand what a professional detection visit looks like.
Evaporation Calculator → Leak Analyzer → Free Beginner Guide →Leak and Subsurface Locators finds structural pool leaks throughout South Florida without draining or unnecessary digging. Licensed CPC1457277. Free estimate before scheduling.
Broward (954) 290-5177 (561) 325-2678 (561) 325-2678Evaporation happens at night but at a much slower rate than during the day. In South Florida, overnight evaporation loss is minimal, typically a fraction of an inch. A noticeable overnight drop of half an inch or more is almost certainly a leak, not evaporation.
Intermittent overnight loss can happen when the leak is close to the current waterline. On nights when the water is slightly higher, it leaks. On nights when it is slightly lower from the previous day's evaporation, the leak point is above the waterline and nothing drains. This intermittent pattern still indicates a leak, it just means the leak is right at the current waterline level.
Yes. The autofill must be off during any water loss observation. If the autofill runs overnight, it replaces the lost water and you will see no drop in the morning, even if the pool lost hundreds of gallons. Turn off the autofill valve before you go to bed and leave it off until after you check the level in the morning.
If your pump runs 24 hours and the pool still drops overnight, both sides of the plumbing are potentially involved. A structural leak drains by gravity regardless of pump state. A pressure-side leak drains faster when the pump runs but can still lose water slowly overnight. We test both states during the visit to separate the sources.