Why is my pool losing water? Evaporation or a leak

Two reasons the water line drops

Every outdoor pool loses water to the air. The City of Scottsdale, which deals with pools in a hot desert climate, lists the main drivers of evaporation as sunlight intensity, air and water temperature, wind, humidity and shading. A UAE summer delivers most of those at full strength, so a noticeable drop in the water line during the hot months is normal.

A leak is different. Water escapes through the shell, a fitting, the pipework or the equipment, and it keeps escaping whatever the weather does.

From the pool deck, both look the same: the water line creeps down the tiles. You cannot tell them apart by looking, and guessing either way costs money. Assume evaporation and a leak keeps running. Assume a leak and you may pay for a search that was never needed. The answer is to measure.

Rule out the obvious first

Before any test, walk round the system with the pump running.

• Look at the equipment. Scottsdale notes that most pool leaks are found at the equipment. Check the pump, filter, valves and unions for drips, and look for wet patches on the ground between the plant room and the pool.
• Look for crust. White, crusty mineral deposits on pipes can indicate a slow leak.
• Find the auto-fill. If the pool tops itself up automatically, the water line may hide a loss completely. Switch the auto-fill off, or close its supply valve, for the duration of any test.
• Check the household meter. DEWA suggests a simple leak check twice a year: switch off all water devices and watch the meter. If it still runs, there is a leak somewhere in the pipes or system. If your pool top-up is fed from the same supply, a stuck top-up valve is one thing to rule out.

The bucket test, step by step

The bucket test compares the pool with a sample of the same water exposed to the same sun and wind. Here is the method published by the City of Scottsdale:

1. Stop adding water by hand and switch off the auto-fill.
2. Do not backwash, and avoid splashing water out of the pool during the test.
3. Stand a bucket on a pool step without submerging it, and fill it with pool water to the same level as the pool.
4. Mark the water level inside the bucket and the pool level on the tile, for example with a wax pen.
5. Wait at least two to three days. If it rains or turns very windy, you may need to start again.
6. Compare. If both levels fall by the same amount, the loss is evaporation. If the pool has fallen more than the bucket, the pool is leaking.

To separate the structure from the plumbing, repeat the test once with the equipment running and once with it switched off. If more water is lost with the pump running, the plumbing is the more likely cause.

Overflow and infinity pools

On an overflow or infinity pool, the water in the pool sits at the edge and the balance tank absorbs the changes. The level to watch is usually the one in the tank, so a specialist will normally measure the loss there rather than with a bucket on a step.

What the result usually points to

• Pool and bucket fall equally. Evaporation. DEWA recommends covering the pool to reduce water lost this way.
• Pool falls more than the bucket. A leak is likely.
• More loss with the pump running. This often points to pipework on the pressure side or to the equipment.
• Similar loss with the pump on and off. This often points to the shell or to fittings set into it.

Some specialists also let the level drop (with the auto-fill off) to see where it stops. LeakTronics, a maker of leak detection equipment, explains that a level that stops at the skimmer, a light or a return fitting gives a strong hint about the leak. Do not let the level fall below the skimmer opening while the pump runs. Pentair's filter manual lists a low water level as a common way for air to enter the system.

When to call a leak detection specialist

Call a specialist when:

• the bucket test shows the pool losing more than the bucket
• you see damp patches on walls, in the plant room or in a unit below
• tiles are lifting or the shell shows new cracks alongside water loss
• you are topping up regularly and cannot explain why

For rooftop and podium pools, treat any suspected leak as urgent, because water escaping from the pool can reach the structure and the units below.

In LeakTronics' field experience, the skimmer is the most common leak point, followed by plumbing, light niches and return fittings. A specialist will check those first, then test the lines.

What to note down before the visit

The first questions a specialist asks are how much water the pool loses per day and how long it has been happening. Keep a dated log of the water line, record the bucket test with the pump on and off, and photograph anything wet or cracked. That information shortens the search.