Every pool loses water. The question is whether yours is losing more than it should, and that is genuinely hard to judge by eye — which is why so many people either top up a leaking pool for years or pay to investigate a pool that is behaving perfectly normally.
There is a simple test that settles it, and you can do it yourself this week.
The bucket test
The principle is neat: evaporation acts on any open water surface at the same rate, so a bucket of pool water sitting in the pool is a control sample. Whatever the bucket loses is evaporation. Anything the pool loses beyond that is a leak.
- Fill the pool to its normal level.
- Take a bucket — a plastic one, five litres or larger — and fill it with pool water to about 30 mm below its rim.
- Stand the bucket on a step in the pool so it is partly submerged. This keeps the water in the bucket at roughly the same temperature as the pool, which matters more than people expect. Weigh it down with a brick if it wants to float.
- Mark both levels — the water level inside the bucket and the pool level outside it — with tape or a waterproof marker.
- Turn off the pump, the auto-fill and any water features, and don't let anyone swim.
- Wait 24 hours, then compare.
If both levels dropped by the same amount, that is evaporation and your pool is fine. If the pool level dropped noticeably more than the bucket, water is leaving somewhere it shouldn't.
Do it twice if you can — once with the pump running, once with it off. If the loss is worse with the pump running, the leak is on the pressure side of the plumbing. If it is worse with the pump off, suspect the shell, the skimmer or the main drain. That single comparison narrows the search enormously.
What is normal on the Sunshine Coast
Evaporation depends on air temperature, water temperature, humidity, wind exposure and sun. For an uncovered pool in south-east Queensland, typical loss runs somewhere around 3–6 mm a day in summer and considerably less in winter — more if the pool is windy and exposed, much less if it is covered.
A useful way to think about it: an uncovered pool losing around 25 mm a week in summer is unremarkable. The same pool losing 25 mm a day is losing thousands of litres a month and needs looking at.
Two things skew the reading. A pool cover cuts evaporation dramatically, so a covered pool that still drops is much more suspicious. And splash-out from swimming and children genuinely accounts for a surprising volume — which is why the bucket test asks you to keep everyone out.
The five places pools actually leak
The skimmer box throat. The most common leak of the lot. The joint between the plastic skimmer and the concrete shell cracks as the two materials move at different rates. The give-away is a pool that stops dropping once the level falls below the skimmer mouth.
The light niche. The conduit entering the light housing is a direct path out of the shell, and the seal around it is a known failure point on older pools.
Underground plumbing. Suction and return lines running under paving or garden. These are the expensive ones to find by digging and the easiest to confirm by pressure testing — each line is isolated and pressurised, and a line that will not hold pressure has been identified without lifting a paver.
The main drain and its fittings. Less common, harder to reach, and usually diagnosed by elimination once everything else has been ruled out.
Cracks in the shell, or failures in the interior finish. Structural cracking, tile and grout failure around waterline tiles, delamination in fibreglass, or perished sealant in the movement joint between coping and shell.
How a leak gets located without demolition
Once the bucket test says there is a leak, the job is to find it without excavating a garden on a hunch.
Pressure testing isolates each line — skimmer, returns, main drain, cleaner line — and pressurises it individually. This is the fastest way to separate a plumbing leak from a shell leak, and it is usually the first thing done.
Electro-acoustic listening picks up the sound a pressurised leak makes underground. Ground microphones follow the pipe run and the loss is pinned to a length of pipe rather than a general area.
Dye testing confirms a suspected shell or fitting leak. With the pump off and the water still, dye released near a crack or a skimmer throat is drawn into the defect visibly.
Thermal imaging and moisture mapping find where the escaped water has gone — under paving, into a retaining wall, into a neighbouring structure. On a pool built over or beside habitable space, this matters as much as finding the leak, because that water is doing damage somewhere.
Pipe and cable locating maps the plumbing runs first, where the original layout is unknown or the plans are long gone.
Why it is worth doing sooner
A leaking pool is not only a water bill. Water escaping under a pool shell or into fill can undermine bedding, move paving, and saturate adjacent structures — and a leak beside a retaining wall or above a basement is a structural problem with a pool attached to it, not a pool problem.
The leak also does not stay the same size. A cracked skimmer throat or a perished joint gets worse, and the repair gets larger with it.
Before you call anyone
Do the bucket test. It costs nothing, it takes a day, and it turns "I think we're losing water" into a number. If the pool matches the bucket, spend the money on a cover instead. If it doesn't, you will already know roughly where to look — and whether the loss changes with the pump running is the single most useful thing you can tell whoever comes out.
More on how we approach it on our swimming pool leak detection page, or send us your bucket test result and we will tell you what it points to.