Pool leak or evaporation? How to tell in Phuket and what to do next

Why pools in Phuket lose water

Pools in Phuket and across Thailand lose a noticeable amount of water to evaporation. This is especially true in the dry season, with strong sun, warm water and a steady breeze. Overflow pools usually lose more than skimmer pools, because the water spreads thinly over the edge and runs along an open channel. Heavy use, splashing and backwashing the filter also take water out.

A leak is different. Unlike evaporation, it does not stop when the weather changes, and it can get worse over time. Some leaks show when the pump is running or when the water stands above a certain level. A leak can wash away treatment, soften the ground under terraces and damage the finish from behind. The aim is to tell the two apart before anyone breaks a tile.

A simple bucket comparison

You can get a useful first answer yourself. Put a bucket on a pool step so that it sits partly in the water, with a stone or brick inside so that it cannot float or tip. Fill it with pool water to roughly the same level as the pool. Mark the water level inside the bucket, and on the pool wall or skimmer.

Leave both for the same period, with no swimming, no backwashing and the automatic top-up switched off. Then compare the drop. Sun and wind act on both in much the same way. If it rains during the comparison, start again; in the wet season, wait for dry days. If the pool has dropped noticeably more than the bucket, water is probably escaping somewhere.

It helps to repeat the comparison once with the pump running and once with it switched off. If the pool loses more with the pump on, that can point towards the pressure-side pipework or the overflow system. If it loses more with the pump off, the suction side is suspect: under vacuum a parted suction pipe draws in air instead of losing water, and you may see air in the pump basket or bubbles at the returns. If the loss is similar either way, the shell, a fitting or a light niche becomes more likely. Treat the result as a pointer, not a diagnosis.

In an overflow pool the surface is held at the edge while the pump runs, so with the pump on, mark and compare the level in the balance tank instead. With the pump off, the water settles below the edge and can be marked in the pool.

What you can see for yourself

Other signs can point to a leak before the bucket does.

None of these proves a leak on its own, but two or three together are worth investigating. Write down what you notice and when, as it helps narrow the search.

One warning. If there is water in the pump room, do not go in while the power is on. Have the supply isolated first, and have the pumps, lights and earthing checked by a licensed electrician before anything is switched back on.

• The automatic top-up runs all the time, or the water bill or delivery orders rise for no clear reason
• Damp patches, soft ground or sinking paving around the pool or near pipe runs
• Hollow or lifting tiles, cracks in the shell or open joints along the terrace
• Water in the pump room or around the balance tank
• A water level that always settles at the same point, such as just below a light or a fitting
• Staining, or algae that keeps returning along one crack or joint

Where to look for a leak

A leak investigation concentrates on a few places where water can escape. In our experience, water most often escapes through pool light fittings, because their conduits are frequently run through the shell instead of being brought up properly above water level.

We also check skimmers, main drains and return fittings, because the seal around them can fail.

• Underwater light fittings and niches. In our experience, light housings, cable glands and conduits run through the shell are the most frequent source of leaks.
• Buried pipes. Pipes under the floor or around the shell can come apart at the joints or crack, for example where the ground has settled.
• Construction joints. The joint between the floor and the walls, or between an old shell and a later extension, can be a weak point.
• Overflow channels and balance tanks. An underground balance tank can seep into the surrounding ground without anyone seeing it.
• An overflow level set too high. When rendering or refinishing raises the overflow edge, the water can rise into the joint under the terrace and escape there.

What a leak inspection involves

Before breaking any tiles or concrete, we inspect the pool, the balance tank and the plant room. We use imported fluorescent leak-detection dye kits: dye is added near suspected points and traced with a special torch. We do everything we can to find the cause by working through likely faults and testing them, but we cannot promise to find every leak; sometimes a leak cannot be found without excavation or opening parts of the structure.

Once a fault is confirmed, we choose the repair that fits it. An overflow lip set too high can sometimes be corrected with the water lowered. We do not reseal leaking lights: we replace them and correct the faulty conduits, with the electrical work agreed with your electrician or engineer. Floor pipes, construction joints, shell waterproofing and tank-in-tank rebuilds (for balance tanks and, in difficult cases, the pool itself) need the pool or tank drained and dried. Draining is planned with the season and the groundwater in mind: an empty shell in waterlogged ground is at risk from the water pressure beneath it, and in the wet season the structure is slow to dry. Decisions on structural repairs such as a tank-in-tank rebuild are taken with you and your engineer — or, if you don't have one, with our partner engineer.

When a pool's history is unknown, not every hidden problem can be found at once. Repairs and restarts can go in stages: fix a fault, start the pool, and check whether another issue shows up. If you want a broader picture first, our pool inspection records any signs of a leak in a written report.

• Evaporation-versus-leak comparisons and water-level checks with the pump on and off
• Fluorescent dye testing traced with a special torch around light fittings, skimmers, drains and return fittings, with water in the pool
• Pressure testing of the suction, return, jet and drain lines
• Checking the overflow level against the terrace joint
• Inspecting underground balance tanks and pump rooms for seepage

Why a new finish is not waterproofing

It is tempting to think that refinishing a pool will seal it. It does not. A finish, whether tiles or PebbleCrete, is a surface layer. Waterproofing is a separate system that sits beneath the render and the finish. Leaks in pipes, lights and tanks are outside the finish altogether.

Refinishing over an active leak hides it for a while. Meanwhile the water keeps escaping, the ground can keep softening and the new surface can be damaged from behind. Find and repair the leak first, then plan the surface.

The same applies to waterproofing. Where a shell or balance tank needs it, waterproofing is its own item of work, planned with the pool or tank drained. It is not something a new finish provides.

What to send us for a first discussion

Send us these details so we can review the symptoms and plan an inspection.

• Photos of the pool, the overflow channel, the balance tank and the pump room
• Your villa, hotel or resort location in Phuket or elsewhere in Thailand
• The approximate pool size, and how much the level drops with the pump on and off
• What you see: damp patches, hollow tiles, cracks, water in the pump room or past repairs