How to Detect and Fix a Pool Leak

Is it actually a leak, or just evaporation?

This is the first question to answer, because a lot of "my pool is leaking" concerns turn out to be completely normal evaporation, especially in hot, dry, or windy weather. Roughly a quarter to half an inch of water loss per day is typical evaporation in warm conditions. Losing noticeably more than that, or losing water steadily even in mild weather, is the signal that something's actually leaking rather than just evaporating off.

The bucket test

The classic, reliable way to tell the difference:

1. Float a bucket in the pool

   Partly fill a bucket with pool water and float it in the shallow end, weighted enough to float low but not sink.

2. Mark both water levels

   Mark the water level on the inside of the bucket, and mark the pool's water level on the outside of the bucket at the same height.

3. Wait 24 hours

   Leave the pump running normally, as you would any other day — don't change your routine for the test.

4. Compare the two marks

   If the pool's water level has dropped noticeably more than the level inside the bucket, the difference is a leak — the bucket accounts for evaporation alone, so anything beyond that gap is water actually escaping the pool.

Where leaks usually hide

Skimmer & light fittings

Common leak points where the fitting meets the pool shell — check for cracking or gaps around the edges.

Equipment pad plumbing

Look for wet or unusually soft ground near the pump, filter, or heater — a sign of an underground pipe leak nearby.

Liner tears (vinyl pools)

Small tears, often near steps, ladders, or the waterline where the liner sees the most wear and UV exposure.

Pump seals

A pump losing water from its own housing rather than the pool itself — check around the pump body and unions for dampness.

Narrowing it down further

A dye test helps confirm a specific fitting: with the pump off so the water is still, release a small amount of dye near a suspected spot underwater — if there's a leak there, you'll see the dye visibly pulled toward it. Comparing water loss with the pump running versus off is also revealing: losing water only while the pump runs points to a pressure-side plumbing leak somewhere after the pump; losing water at roughly the same rate regardless of whether the pump is on points to a structural leak in the shell, liner, or a fitting instead.

Why it's worth fixing promptly

Beyond the obvious water cost, an ongoing leak dilutes chemical levels as leaked water gets replaced with fresh top-up water, which is why a leaking pool often seems to need more frequent rebalancing than usual — see our cloudy water guide if that's also part of what's going on. Left long enough, a structural or plumbing leak can also undermine surrounding decking or erode the ground around the shell, turning a manageable repair into a much bigger one.

When to call a professional

Underground plumbing leaks are genuinely difficult to pinpoint without specialist equipment (acoustic listening devices, pressure testing), and extended DIY guessing often costs more in wasted time and water than just calling a professional leak detection service. If the bucket test confirms a leak but you can't visually locate it within a reasonable amount of looking, that's the point to bring someone in rather than keep searching.

If water loss consistently stops right around the skimmer opening, see our skimmer-specific leak guide for the exact spots to check.

Common questions