Swimming pools leak at a handful of usual points: the skimmer, the liner or shell, the return lines, the buried pipework, the light niche and the valves at the equipment pad. The skimmer is often cited as the most common, because it is a joint where plastic meets the pool, and ground movement opens a gap there.
A pool that keeps dropping is frustrating, partly because the water gives so little away. The level falls, the bill climbs, and the leak could be anywhere. The good news is that pools do not leak randomly. They leak at a short list of weak points, and once you know that list you can narrow things down quickly. This guide walks through where pools lose water and what each spot looks like, so you know where to point your attention first. If you still need to confirm there is a leak at all, start with our guide on how to tell if your pool is leaking, then come back here to find the source.
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First, is it really a leak?
Before you go looking for a leak point, rule out plain evaporation. A pool can shed around a quarter of an inch of water a day to evaporation in warm, breezy weather, and more if it has no cover. Steady loss above that level is the sign that water is escaping somewhere rather than just lifting off the surface. The quickest way to be sure is the bucket test, which sits a bucket of pool water beside the pool and compares how far each one drops over a day. We cover that step by step in how to tell if your pool is leaking. Once you know there is a genuine leak, the spots below are where to look.
The skimmer
The skimmer is the basket-shaped opening at the waterline that pulls surface water into the filter. It is often the first suspect, and for good reason. The skimmer is a plastic unit set into a pool built from concrete, gunite, fibreglass or vinyl, so there is a joint where two different materials meet. As the ground around the pool settles, freezes or shifts, that joint can crack or pull apart, and water seeps out where the skimmer meets the pool wall.
A telltale sign is a pool that drops only until the water falls below the skimmer mouth, then holds steady. That points the finger straight at the skimmer throat or its connection to the wall. A dye test around the skimmer mouth, done with the pump off, shows whether the dye is being drawn into a crack.
The liner or shell
The thing actually holding the water can leak too. On a vinyl-liner pool, the liner is most likely to tear or split where it is stretched or sealed: corners, steps, and the gaskets around the skimmer, returns and lights. A pinhole in a liner can be tiny and still lose a lot of water over a week. On a concrete, gunite or fibreglass pool, the shell itself can crack along seams, around fittings, beneath the coping stones, or through the structure where the ground has moved.
Liner leaks sometimes show as a small wrinkle, a stain, or a patch of softer ground behind the wall. Shell cracks can be hairline and hard to spot with the eye, which is where professional detection earns its keep.
Return lines and fittings
Return lines are the pipes that carry filtered water back into the pool, and the return fittings are the eyeball jets you feel pushing water as you swim. Because these lines run under pressure when the pump is on, even a small crack or a loose fitting pushes water out steadily. Leaks here tend to sit where the pipe meets the pool wall, at the fitting itself, or along the buried run as the ground settles.
If the pool loses more water with the pump running than with it off, a pressure-side return line is a strong candidate. That pump-on versus pump-off difference is one of the more useful clues you can gather yourself before calling anyone out.
Underground pipework
Plenty of a pool's plumbing is buried, and buried pipes leak out of sight. Suction lines (which pull water toward the pump) and pressure lines (which push it back) can crack, corrode or separate at joints as the soil moves over the years. The water escapes into the ground with nothing obvious at the surface.
Clues to a buried pipe leak include soggy or sunken ground near the pipe runs, an oddly green patch of lawn, air bubbles in the pump basket, or the pump struggling to prime. Because there is nothing to see, this is one of the hardest leaks to place without equipment. Acoustic listening gear can hear water escaping a pressurised line, and a pressure test isolates which run has failed, so you dig in one spot rather than trenching the whole garden. The same buried-pipe detective work applies to ordinary water leak detection around the home.
The light niche
An underwater light sits in a recessed housing called a niche, with a conduit carrying its cable back to a junction box. Two things leak here. The seal where the niche meets the pool wall can fail, and the conduit running from the niche can crack or pull away, letting water travel along the cable route and out into the ground. On a liner pool, the gasket around the light is another sealed point that can give way.
A dye test around the rim of the light niche, pump off, usually reveals a niche-seal leak. A conduit leak is sneakier, because the water disappears down the cable run rather than pooling at the light.
Valves and the equipment pad
Not every pool leak is in or under the pool. The equipment pad, where the pump, filter, heater and valves live, has dozens of connections and any of them can weep. Multiport valves, unions, the filter housing and the pump seal are common offenders. A leak here is often the easiest to find, because it is above ground and you can usually see or feel the drip while the system runs.
Walk the pad with the pump on and look for damp patches, drips, or mineral staining around fittings. If the ground under the equipment is wet but the pool holds its level overnight with the pump off, the pad is the place to focus.
Reading the water level for clues
Where the water stops dropping is one of the best free clues you have. Let the pool find its own level over a day or two with the pump off and note where it settles.
| Where the water settles | Likely leak point |
|---|---|
| Drops to the skimmer mouth, then holds | The skimmer throat or its joint with the wall |
| Stops level with a return jet or the light | That return fitting or the light niche |
| Keeps dropping below all fittings toward the floor | The main drain, a floor fitting, or the shell |
| Loses more with the pump on than off | A pressure-side return or buried pipe run |
| Loses more with the pump off than on | A suction-side line or the skimmer |
This narrows the search, but it rarely pinpoints the exact spot, especially with buried pipes or a hairline shell crack. That final step is what specialist detection is for.
Pool leak detection in Cornwall & Devon
Across Cornwall and Devon we trace pool leaks with non-invasive equipment: acoustic listening for water escaping under pressure, dye testing at fittings, and pressure testing to isolate a failed pipe run. That means we locate the source before anything is dug up or opened, so the repair is targeted rather than a guess. If you have confirmed a leak with the bucket test and the level clues above, our pool leak detection service takes it from there and finds exactly where your pool is losing water. You can also read more about the methods we use to tell whether a pool is leaking in the first place.
Frequently asked questions
Where do swimming pools leak most often?
The skimmer is often cited as the most common spot, because it is a joint where plastic meets the pool shell and ground movement can open a gap. Return lines, the light niche, underground pipework, the liner or shell, and the valves at the equipment pad are the other usual culprits.
How do I know my pool is leaking and not just evaporating?
A pool can lose around a quarter of an inch a day to evaporation in warm weather. Steady loss above that points to a leak. The bucket test compares pool loss with a bucket of pool water side by side, which separates evaporation from a real leak before you start hunting for the source.
Does the water level tell me where the leak is?
Sometimes. If the level drops and then settles at the skimmer mouth, the leak is likely around the skimmer. If it stops at a light or a return fitting, suspect that point. If the pool keeps dropping below all fittings to the floor, the leak is more likely in the main drain or the shell.
Can a swimming pool leak underground without me seeing it?
Yes. Buried suction and pressure pipes can crack or pull apart at joints as the ground settles, and the water escapes into the soil with nothing visible at the surface. Soggy ground near the equipment pad, an unusually green patch of lawn, or air in the pump basket can all hint at a buried pipe leak.
Will a pool leak get worse if I leave it?
Usually yes. Escaping water washes away the ground supporting the pool and pipework, so a small leak tends to grow and can undermine paving or the shell. Finding it early keeps the repair small. A specialist can pinpoint the source with minimal digging rather than guesswork.
How does a professional find a hidden pool leak?
With non-invasive equipment. Acoustic listening picks up the sound of water escaping under pressure, dye testing confirms suction leaks at fittings, and pressure testing isolates which pipe run has failed. That combination locates the leak before anything is opened up, so the repair is targeted rather than exploratory.
Pool losing water and you can't find where?
We trace swimming pool leaks across Cornwall & Devon with acoustic, dye and pressure testing, so we find the source with minimal digging. Fast response, fixed upfront pricing, no call-out fee.
Call Dickie on 07822 025 911 No Find, No Fee on residential leak detection (subject to terms)