Is Your Pool Actually Leaking?
Before spending money on professional leak detection, it is worth confirming that your pool is actually losing water to a leak rather than to evaporation. In the warmer months, a swimming pool in London can lose between 3 and 7 millimetres of water per day through evaporation alone. On hot, windy days, this can be even higher. If your pool is losing significantly more than this, or if it continues to lose water at the same rate during cool, calm weather, a leak is the likely cause.
The pool industry uses a simple and effective test to distinguish between evaporation and a genuine leak. It is called the bucket test, and you can do it yourself before calling in the professionals.
The Bucket Test: A Simple DIY Check
Here is how to carry out the bucket test:
- Fill a bucket with pool water and place it on the pool steps or a bench inside the pool, so the bucket is partially submerged but stable
- Mark the water level inside the bucket and the water level in the pool on the outside of the bucket, or on the pool wall
- Leave the bucket for 24 hours. Do not use the pool during this time, and do not top up the water
- After 24 hours, compare the two levels. Both the bucket water and the pool water will have evaporated at the same rate. If the pool water level has dropped more than the bucket water level, you have a leak
For an even more informative test, repeat the experiment twice: once with the pump and filtration system running, and once with everything turned off. If the pool loses more water when the pump is running, the leak is likely in the plumbing or filtration system. If the loss is the same regardless, the leak is more likely in the pool shell or fittings.
Where Pool Leaks Occur
Pool leaks can be categorised into three main types based on their location:
Shell Leaks
These are cracks or failures in the pool structure itself. In concrete pools, they may be caused by ground movement, freeze-thaw damage, or age-related deterioration of the render or tiling. In fibreglass pools, delamination or impact damage can create leak paths. In vinyl-lined pools, tears, punctures, or failed seams in the liner are the usual culprits.
Fitting Leaks
Leaks frequently occur at the points where fittings penetrate the pool shell. This includes return jets, skimmer boxes, main drain fittings, underwater lights, and any other through-wall fittings. The sealant or gasket around these fittings can deteriorate over time, allowing water to seep through.
Pipe Leaks
The pipework connecting the pool to the pump room can also develop leaks. These pipes are typically buried in the ground and are subject to ground movement, root damage, and connection failures. Pipe leaks are often the most difficult to locate because the pipes are not visible.
Professional Detection Methods
Dye Testing
Dye testing is a simple but effective technique used to confirm leak locations in the pool shell and around fittings. The engineer uses a syringe to release a small amount of coloured dye near a suspected leak point. If a leak is present, the dye will be drawn towards and into the crack or gap by the flow of escaping water. This is a very precise method that can identify exactly which fitting or crack section is leaking.
Dye testing is typically done with the pool full and the pump turned off, so the water is completely still. The engineer works their way around all fittings, joints, and any visible cracks, testing each one individually.
Pressure Testing
Pressure testing is used to check the pool plumbing. Each pipe is isolated and pressurised independently. If a pipe cannot hold pressure, it is leaking. The rate of pressure drop gives an indication of the leak severity, and in some cases, acoustic methods can then be used to locate the exact point on the pipe where the leak is occurring.
The pipes that are typically tested include the suction lines from the skimmers and main drain, the return lines to the jets, and any auxiliary lines for features like fountains or heating.
Acoustic Detection
For underground pipe leaks, acoustic leak detection equipment can be used in the same way as it is for domestic water supply pipes. Ground microphones are placed along the pipe route to listen for the sound of water escaping. This method is most effective when the pipe can be pressurised and the surrounding ground is relatively quiet.
Electronic Leak Detection
For vinyl-lined pools, a specialist technique called electronic leak detection can be used. This involves passing a low-voltage electrical current through the pool water. Because vinyl is an insulator, the current is drawn towards any breach in the liner where it can reach the conductive material beneath. A sensor moved across the pool surface detects these current concentrations, identifying the exact location of even tiny holes in the liner.
Common Pool Leak Symptoms
- Needing to top up the pool more than once a week during normal weather
- Air bubbles in the return jets when the pump is running, which can indicate a suction-side pipe leak
- Cracks in the pool deck or surrounding paving, caused by water eroding the sub-base
- Soggy or eroded ground around the pool area
- Algae growth that is difficult to control, because the constant addition of fresh water dilutes the chemical balance
- Higher than expected water bills if the pool is connected to a metered supply
Costs for Pool Leak Detection in London
Pool leak detection in London typically costs between 350 and 750 pounds depending on the size of the pool and the complexity of the investigation. This includes dye testing of all fittings, pressure testing of the plumbing, and a full report. Acoustic detection of underground pipes, if required, may add to the cost.
Repair costs vary widely depending on the type and location of the leak:
- Fitting seal replacement: 100 to 300 pounds
- Pipe repair (accessible): 200 to 500 pounds
- Pipe repair (buried): 500 to 1,500 pounds
- Shell crack repair: 300 to 1,000 pounds
- Liner repair or replacement: 200 to 3,000 pounds depending on size
Given the cost of water, chemicals, and potential structural damage, investing in professional leak detection for your London pool is almost always worthwhile when you suspect a problem.