Swimming Pool Leak: How to Find and Fix It

Losing water from your pool doesn’t have to mean trouble

You glance at the pool one morning and the water line looks a little lower than you remember. Then it happens again the next week. It’s natural to start worrying about a swimming pool leak, and the costly repair you imagine might follow.

Take a breath. Pools lose water for all sorts of reasons, and many of them are perfectly normal. Even when there is a real leak, it’s usually small, easy to trace and much simpler to fix than people fear.

In this guide we’ll walk you through how to tell normal water loss from a genuine problem. We’ll show you two simple tests you can do yourself, where leaks tend to hide, and which jobs are safe to tackle on your own.

We’ll also be honest about when it’s time to hand things over to a professional. Catching a problem early is always kinder to your pool, your garden and your water bill.

A quick word on one-piece pools

We install one-piece pools, which are made as a single moulded shell. There are no joins or seams in the pool body for water to escape through. That means when one of our customers spots water loss, the shell is rarely the cause. It’s far more likely to be something connected to it, like a pipe joint or a light fitting. We’ll come back to that later.

A dropping water level isn’t always a swimming pool leak

Before you start hunting for holes, it helps to know how much water a healthy pool loses on its own. Some loss is completely normal, and it can vary a lot from week to week.

Evaporation is the most common culprit

Water evaporates from the surface of every pool, every day. On a warm, sunny, breezy day it can be surprisingly quick. As a rough guide, a few millimetres a day is not unusual in hot or windy weather, and a little more if the water is heated.

A few things speed evaporation up:

• Warm, dry air and plenty of sunshine
• Wind blowing across the surface
• Heated water, especially on cool evenings
• Water features, fountains and overflow edges that stir the surface
• Leaving the pool uncovered overnight

A good cover makes a big difference here. It keeps warmth in and stops a lot of water escaping into the air. If you heat your pool, our guide to swimming pool heating explains how covers and heating work together.

Everyday use takes water too

Splashing, cannonballs and wet swimmers climbing out all carry water away. So does backwashing your filter, which sends water to waste on purpose. A busy weekend with the grandchildren can easily knock the level down noticeably.

Rain can hide what’s really happening

In a wet spell, rainfall can top the pool up and mask a slow leak. Then the weather turns dry and suddenly the level falls faster. That doesn’t always mean something has broken. It may just be that the rain was covering a normal pattern.

The bucket test tells you whether you really have a leak

The bucket test is the easiest way to separate evaporation from a genuine loss. The idea is simple. A bucket of pool water sitting in the same spot should evaporate at the same rate as the pool itself. If the pool drops noticeably more than the bucket, something else is going on.

How to do the bucket test

1. Top your pool up to its normal operating level.
2. Fill a bucket with pool water to roughly the same height as the pool water outside it.
3. Stand the bucket on the pool step or first ledge so it sits in the water. Weigh it down with a brick or a couple of stones if it wants to float.
4. Mark the water level inside the bucket with tape or a marker pen.
5. Mark the pool water level on the outside of the bucket, or on the skimmer faceplate.
6. Switch off any auto-fill so the pool isn’t being topped up in the background.
7. Leave everything alone for 24 hours, without swimming or backwashing.
8. Compare the two drops.

Reading the results

If both levels have fallen by about the same amount, you’re almost certainly just seeing evaporation. Nothing to worry about.

If the pool has dropped clearly more than the bucket, you likely have a leak worth looking into.

It’s worth repeating the test a second time, once with your pump running and once with it switched off. If the pool loses more water while the pump is running, the problem is often in the pressure side of your pipework, after the pump. If it loses more with the pump off, the suction side is a likelier suspect. It’s not a hard rule, but it’s a helpful clue.

Most swimming pool leak problems start in the pipework, not the shell

When a leak is confirmed, most people picture a crack in the pool itself. In reality, the shell is often the least likely place to look. Water tends to find its way out through the parts that connect to the pool, because these have joints, seals and moving water.

Pipework and joints

Pipes run underground between your pool and the plant room. Over time, ground movement, frost or a poorly made joint can let water seep out. Leaks here can be slow and hard to spot, but they often show up as damp patches or soft ground along the pipe route.

Fittings in the pool wall

Every opening in the pool needs a watertight seal. That includes:

• Skimmers, which are a very common source of small leaks where they meet the shell
• Return jets that push filtered water back into the pool
• Main drains in the floor
• Any cleaning or suction points

Gaskets and sealants age with sun, chemicals and temperature changes. A tired seal is usually a quick, inexpensive fix once it has been found.

Underwater lights

Lights sit in a housing set into the pool wall, with a cable running out to the plant room. The seal around the housing, or the conduit carrying the cable, can let water escape. Because electricity is involved, this is always a job for a qualified professional.

Equipment in the plant room

Pumps, filters, heaters and valves all have seals and unions that can weep. Take a look around your plant room for drips, puddles, salt or scale deposits and rust stains. A leak here won’t lower the pool quite as mysteriously, because you can usually see it.

A dye test can help pinpoint where water is escaping

Once the bucket test confirms a swimming pool leak, a dye test can help narrow down the spot. It works because leaking water gets drawn towards the gap, and a small puff of coloured dye will follow it.

How to do a dye test

1. Switch the pump off and let the water settle until it’s completely still. Any movement will scatter the dye.
2. Use a proper leak detection dye, which you can buy from pool suppliers. It usually comes in a small bottle or syringe.
3. Put on goggles or a mask if you need to get close to the wall.
4. Gently release a small amount of dye right next to the place you suspect, such as the edge of a skimmer, a return jet or the rim of a light.
5. Watch closely. If the dye drifts away and hangs in the water, there’s no leak there. If it’s pulled towards the fitting and disappears into it, you’ve probably found your culprit.

Tips for getting it right

• Go slowly and test one fitting at a time.
• Start with the most likely places, like skimmers, returns and lights.
• Test around the whole perimeter of each fitting, not just one side.
• Don’t use food colouring, as it can stain and spread too quickly to be useful.

If the dye tells you nothing and the bucket test still shows water loss, the leak is probably in buried pipework. That needs professional equipment to find, which we’ll cover next.

Some fixes are simple, others need a professional

A lot depends on where the leak is and what your pool is made of. Here’s an honest view of what you can safely do yourself and what’s better left to us.

Jobs you can often tackle yourself

• Plant room drips. Tightening a hand-tightened union or replacing an O-ring on a pump lid is often straightforward. Always switch the power off first.
• Small liner tears. If you have a liner pool, you can often use an underwater patch kit without draining. Follow the kit’s instructions carefully.
• Keeping an eye on things. Noting the water level every few days helps you spot a pattern early.

Jobs that need an expert

• Anything electrical, such as underwater lights or wiring. Never try to open a light housing yourself.
• Buried pipework. Specialist leak detection uses pressure testing, listening equipment and cameras to find leaks without digging up your whole garden.
• Structural concerns in concrete or tiled pools, such as cracks or loose tiles. These need proper assessment.
• Seals in the pool wall, where the repair must bond reliably to the shell.

Please don’t drain your pool to look for a leak

This one is important. Emptying a pool can be risky, particularly for one-piece shells. With the weight of the water gone, pressure from groundwater underneath can push the shell upwards or move it out of shape. Always speak to a professional before lowering the water much below its normal level.

Why leaving it rarely pays off

A small, steady swimming pool leak might seem harmless. But the water has to go somewhere. Over time it can soften the ground around your pool, affect paving and wash away the backfill supporting the shell. Topping up constantly also dilutes your chemicals, which can upset your pool pH and make it harder to keep the water clear. It adds to your pool running costs too, with extra water, heat and chemicals being lost.

The good news is that most leaks found early are quick fixes. It’s the ones left for a season or two that become bigger jobs.

Swimming pool leak questions we get asked a lot

How much water loss is normal?

It depends on the weather, whether the pool is heated and whether it’s covered. A few millimetres a day in warm, windy spells is fairly typical, but the bucket test is the best way to know for sure.

Can a pool leak through the skimmer?

Yes, and it’s one of the most common places. The seal between the skimmer and the pool shell can wear over time. A dye test around the skimmer is a good first check.

Will a leak damage my garden?

It can if it’s left alone. Escaping water can soften the soil, lift paving or create damp patches. Getting it checked early keeps things simple.

Can you find a leak without digging?

Usually, yes. Professional leak detection uses pressure testing and listening equipment to trace leaks in buried pipes, so any digging is kept to a small, targeted area.

Is it safe to swim if my pool is leaking?

In most cases a slow leak doesn’t make swimming unsafe. The exception is anything near underwater lights or electrics. If you’re unsure, stay out and give us a call.

Do you repair pools you didn’t install?

We’re always happy to talk it through. Get in touch with a few details about your pool and we’ll let you know how we can help.

We’re here to help with any swimming pool leak

Most leaks sound far worse than they are. With a bucket test, a dye test and a careful look around your plant room, you can often work out what’s going on in a day or two. And if you can’t, that’s exactly what we’re here for.

We offer aftercare, servicing and repairs for our customers, so you’re never left to deal with a problem on your own. Our team knows one-piece pools inside out, and we’ll find the cause quickly and fix it properly. If a repair is needed, we’ll give you a clear, tailored quote before any work begins.

Thinking about a new pool, or upgrading an old one that’s given you trouble? You can explore our full range of pools and see why so many families choose a one-piece shell.

Call us on 01483 323 676 or email hello@hilifepools.co.uk for a friendly, no-pressure chat, or get in touch online and we’ll come back to you.