How to Find a Leak in Your Pool: A Pro's Guide to Inground Pool Leak Detection

Your pool is losing water. You top it off with the garden hose, and two days later the water level has dropped again. Most guides tell you to squirt food coloring around the walls and hope it points somewhere. That rarely works.

Here is how to find a leak in your pool the way pros think about it. You confirm the loss, narrow it down, then test only the spots that matter. We build pool leak detection equipment at LeakTronics in Agoura Hills, California, and we do leak detection work every day. Below is what you can safely check yourself, and where pro tools take over.

Start Here: 95% of Pool Leaks Are Within 3 Feet of the Pool

Our founder, Darren Merlob, has found that 95% of pool leaks sit within a 3-foot radius of the pool itself. That one fact changes how you search.

It means the leak is almost never out in the yard. It is in the shell, at a fitting, at the skimmer, at the light, or in the pool plumbing right behind the walls. A wet spot 15 feet away may have nothing to do with the pool, because water travels before it surfaces.

Stop chasing puddles and stop pouring food coloring all over the pool. The leak is almost always right there at the pool. Confirm you have one, isolate it, and listen for it. That is the whole job.

So focus on the common spots first. The search gets much smaller when you know where leaks live.

Step 1: Spot the Real Signs of a Leak (and Why We Skip the Bucket Test)

Some water loss is normal. Sun, wind, and low humidity all drive evaporation. The question is whether your pool is losing more than that.

Almost every guide sends you to the bucket test first. You set a bucket of pool water on a step, mark the water inside and the pool water level on the outside of the bucket, and compare a day later. If the pool drops more, the guides say the leak is indeed real.

Darren's advice is blunt: forget the bucket test. Rain, splash, wind, the pump, an auto-fill that kicks on, and even where you set the bucket can all throw off the result. Normal evaporation also changes a lot from place to place. A pool in the desert and a pool near the coast lose water at very different rates.

These signs tell you more than a bucket will:

• You are adding water far more often than you used to.
• The auto-fill runs constantly, or your water bill jumps.
• You need more chemicals than usual to keep the water balanced.
• The pool water level drops noticeably overnight.
• New cracks, loose tile, or soggy ground show up around the pool.

The simplest check is a strip of tape at the tile line. Mark the water each morning to see if the water keeps dropping at the same rate. If it does, you likely have a leak. Note how much water per day you are losing and how long it has been going on. A pro will ask, and it gives them a head start.

Not sure the results add up? Our post on how to know if your swimming pool is leaking covers the warning signs in more detail.

Step 2: Rule Out the Equipment, the Valve, and the Auto-Fill

Before you look in the pool, look at the pool's equipment pad. Equipment leaks are the easiest find of all.

• Check the pool pump. Look for drips at the pump lid, the shaft seal, and the unions.
• Check the filter. A worn gasket or O-ring on a filter tank can drip all day, causing water loss that looks like a pool leak.
• Check every valve. A backwash valve that does not seal can send pool water to waste.
• Check the auto-fill. A broken auto-fill valve can hide a leak or overfill the pool. Turn it off before any test.

Also walk the areas around the pool. Look for soggy soil, sunken pavers, or a crack or gap in the deck. These can point toward the leak area, but keep the 3-foot rule in mind.

Step 3: Let the Water Level Drop and See Where It Stops

This step costs nothing but time. Turn off the auto-fill and let the pool drop. Then mark the water each day.

Where the level stops is a strong clue to the location of the leak:

• It stops at the skimmer. The leak is likely at the skimmer throat or its plumbing.
• It stops at the light. The leak is likely in the light niche or the conduit behind the light.
• It stops at a return fitting. Check that fitting and its line.
• It keeps dropping. The leak may be at the main drain or the bottom of the pool, or in a line under the deck.

Do not drain the pool to look for a leak. In some soils, groundwater can push up on an empty shell. Our guide to hydrostatic testing for pool pipes explains why.

You can also compare loss with the pump on and off. Losing more water with the pump running often points to the pressure side, the return lines. Losing more with the pump off often points to the suction side. A skimmer that starts to gurgle, or air bubbles blowing out of the returns, also hints at a suction leak.

Step 4: Inspect the Skimmer, Pool Lights, and Fittings

Before you inspect or test anything, fill the pool to its normal level and make sure the water is clear. Darren's rule is simple: if you can't see the main drain, the water is not ready.

Now inspect the pool itself. Inground swimming pools leak in the same few places, so put on goggles and look closely at the common spots.

• Around the skimmer. The seam where the plastic skimmer meets the concrete is the number one leak spot we see.
• Pool lights. Check the light housing, the niche, and the cord conduit behind the light. A leak around the light niche is very common.
• Return fittings. Look for cracks around each fitting and missing face plates.
• Steps and benches. Inspect corners and seams for a crack or gap.
• The shell. In a concrete pool, look for structural leaks like long cracks. With a vinyl liner, look for tears, pulled seams, and loose spots around the faceplates.

If you have an above-ground pool or a pool liner, the same idea applies. Look closely at seams, fittings, and anywhere the liner is stretched.

Not sure where to start? A trained tech can do all of this in one visit. Find a pool leak detection pro through our Find A Pro directory, or call LeakTronics at (818) 436-2953.

Step 5: Dye Test the Suspected Spots, Not the Whole Pool

A dye test confirms a leak at one exact spot. It cannot search the whole pool for you.

Here is how to do it right:

1. Turn off the pool pump and let the water go still.
2. Hold a dye syringe within an inch of the suspected leak.
3. Squeeze out a small, slow stream of tracer dye.
4. Watch. If the dye gets pulled into the crack or fitting, water is escaping there.

Put dye near suspected spots only: skimmers and returns, lights, cracks, and fittings. Food coloring clouds out fast and makes a mess, so a real leak detection dye works much better. LeakTronics founder Darren Merlob has written about why food coloring wastes your time in our post debunking the leak detection mysteries.

Step 6: Pressure Test the Suction Lines and Return Lines

If the shell and fittings pass, the leak is likely in the plumbing system. This is where most DIY searches stall, because you cannot see underground plumbing. Pros pressure test last, once everything else has been ruled out.

A pressure test checks one line at a time:

1. Plug the pool end of each line with test plugs.
2. Close the valves at the pad.
3. Fill the line and add low water pressure through a pressure rig.
4. Watch the gauge. If the pressure drops, that line leaks.

Testing the suction and return lines separately lets you test lines to determine which one has the pipe leak. For a full walkthrough, see our guide on how to pressure test pool lines. The main drain leak detection guide covers the hardest line to test.

For pool pros: a leak detection testing kit with plugs and a gauge is how you run this test right. The Master Aqua Plug Kit includes Aqua Plugs, injectors, testing cones, and a pressure rig for every standard pool plumbing size.

How Professionals Find a Leak in Your Pool Without Draining It

A pressure test tells you which line leaks. It does not tell you where. To locate a leak in a buried line, professionals use specialized equipment that listens for it.

Water pushing out of a crack, pinhole, or pipe separation makes a sound. Our listening gear picks it up:

• The Pool Scope. A hydrophone you drop into the water. It listens around fittings, drains, lights, and cracks. As you get closer to the leak, the sound gets much louder.
• The Deck Plate. It listens through concrete, brick, and coping to locate underground leaks beneath the deck.
• The Soil Probe. It listens through soil, landscaping, and gravel to find leaks in underground pipes around the pool.

The goal is to find the leak with the least digging. A tech using this gear rarely needs to dive in the pool or dig blind. They mark the source of the leak, open one spot, and fix it. That is how pros find leaks without draining the pool.

Common Pool Leak Spots and How to Test Them

Can You Fix a Pool Leak Yourself?

Sometimes, for small leaks. Pool putty can seal a small gap around a fitting until a real repair is done. It is a patch, not a cure.

Be careful with cracks. Putty and epoxy do not fix cracks in a pool shell for good. Structural leaks need a proper repair from pool repair pros. Underground plumbing leaks need the line located and repaired, or relined.

If you have already found a pipe leak, trenchless pipe repair can reline the line without digging up the deck. If you still need to figure out where the leak is, a pro saves you time and digging.

Pool Leak FAQ

How much does pool leak detection cost? It depends on the size of the pool, the number of lines, and how hard the leak is to reach. Many leak detection companies charge one fee to test and locate. Ask what is included before the tech arrives.

Why is my pool losing 1 inch of water a day? That is usually far more than normal evaporation, though what counts as normal depends on where you live. If the level keeps dropping that fast day after day, treat it as a leak and have it tested. An inch a day often points to a plumbing leak or a leak at the skimmer.

Can you fix a pool leak without draining? Yes, in most cases. Pros find leaks without draining the pool using a Pool Scope and pressure tests. Many fitting and plumbing leaks can be repaired with the water still in.

What is the most common cause of pool leaks? In our experience, the skimmer is the most common spot, followed by plumbing leaks, light niches, and return fittings. Ground movement and age loosen seals and crack fittings over time.

Get Help Finding Your Pool Leak

You now know how to find a leak in your pool, step by step. Watch for the real signs of water loss. Rule out the equipment. Let the level drop. Inspect and dye test the common spots. Then pressure test the lines.

If you suspect a leak in your inground pool and the simple tests come up empty, call a pro. A trained tech can locate the source in one visit. Find one through the LeakTronics Find A Pro directory, or call us at (818) 436-2953.

Run a pool service or leak detection business? Add leak detection to your services with our pool leak detection kits and the Swimming Pool Pro Equipment Bundle. Every kit comes with online swimming pool leak detection training and support from techs with over 30 years in the field. Before you purchase a pool leak detection kit, book a free 1-on-1 to match one to your jobs.