Start with the bucket test to rule out evaporation. Place a bucket of water on the first step, mark the water level both inside and outside the bucket, and wait 24 hours. If the water in the bucket drops as fast as the pool, it is evaporation. If the pool drops faster, there is a leak.
Next, check whether the level drops differently with the pump on or off. If the pool loses water mainly while the system is running, that points to the pipes or fittings under pressure. If it also drops with everything switched off, the leak is more likely in the shell itself.
Common spots are the skimmer and inlets, the seals around lights, cracks in the floor or walls, and the plumbing. A coloured test dye next to a suspected crack can reveal whether water is being drawn in there.
Pinpointing a hidden leak is skilled work. We assess the situation on site and advise whether a targeted repair is enough or a seamless waterproof finish is the wiser choice. Feel free to request a no-obligation inspection.
The bucket test, step by step
Place a bucket on the first step of the pool, deep enough that it stays put but does not tip over. Fill it with pool water to about five centimetres below the rim. Using a waterproof marker, draw two lines: the water level inside the bucket, and the pool level on the outside of the bucket.
Leave everything for twenty four hours. Run the pump on its normal programme, do not use the pool and do not cover it, because otherwise you are measuring something other than the usual situation. Then compare the two lines.
If both dropped by the same amount, nothing is wrong and your water is simply evaporating. During the summer months on the coast, one and a half to three centimetres a week is entirely normal. If the pool has clearly dropped further than the bucket, you are losing water that should not be leaving.
If in doubt, repeat the test on a day without wind. Wind speeds up evaporation at the pool surface more than inside the bucket and can distort the result.
Pump on or pump off tells you where to look
Run the test a second time, this time with the installation switched off completely. The difference between those two measurements usually points you in the right direction.
If the pool mainly loses water while the pump is running, the pipes are under pressure and water is being forced out where a fitting or a pipe no longer seals. That is nearly always in the pressure line between the plant room and the inlets.
If the level also drops with everything off, the leak is in the shell itself or in a component sitting at water level, such as the skimmer or a light housing. The water usually falls to a certain level and then stops. The leak sits at exactly that height.
If it drops at roughly the same rate with the pump on and off, something in the shell is at fault and it has little to do with the installation.
Where leaks usually turn out to be
The skimmer is by far the most common spot. The joint between the plastic skimmer box and the surrounding concrete moves with temperature changes and eventually cracks open. You often cannot see it because it sits behind the coping.
Next come the light housings. The seal around a light is a rubber that hardens after ten to fifteen years. The inlet nozzles and the main drain are equally common places for a seal to give up.
In the shell itself it is usually hairline cracks, often in a corner or along the steps. They appear because concrete moves and the tile adhesive or grout cannot follow that movement. In a tiled pool the water does not even need a visible crack: it creeps behind the tiles along the grout lines.
Finally there are the buried pipes. Those are the hardest because there is nothing to see. A wet patch in the garden that never dries out, or one strip of grass growing noticeably faster, is sometimes the only clue.
When it is not a leak at all
One backwash of the filter easily costs several centimetres of water height. Anyone who backwashes weekly and counts that as loss is hunting a leak that does not exist.
Splash out adds up too. A pool with children in it every day loses noticeably more than the same pool sitting quietly. An automatic top up makes it treacherous: it refills unnoticed, so you only spot the loss on your water bill.
So always check first how often you backwash, whether the pool tops up by itself, and how heavily it is used. Only once all of that is accounted for and the water keeps dropping is there reason to look further.
Waiting makes it more expensive
A leak is rarely just a water problem. The escaping water carries sand and soil out from under the shell. As a result the pool starts to settle unevenly and a hairline crack grows into a real one.
On top of that, damp concrete attacks the reinforcement, and chlorinated water saturates the surrounding ground. A leak left running for two summers therefore often costs more in repairs than the leak itself would ever have cost.
If you are losing more than roughly one centimetre a day, it is wise not to wait until the end of the season.
Repair, or waterproof it in one go
With one clearly identifiable leak, for example a worn seal around a light, a targeted repair is perfectly fine. Nothing else needs to happen.
If there is more than one leak, or the water runs behind the tiles without you being able to point at where, targeted repairs become a losing battle. Every time you close one spot, the water finds the next weak point.
In that case a seamless waterproof layer across the whole shell makes more sense. It follows the shape of the pool without seams or grout lines, bonds to the substrate so nothing can travel behind it, and moves with the concrete. Expected service life is fifteen to twenty five years.
We locate the leak on site first and then tell you honestly which of the two suits your pool. Sometimes that is simply a half day repair.
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