How to Find and Fix an Inground Pool Leak

Is your water level dropping faster than usual?

If you think you have a leak, there are some steps you can take to confirm, identify, and even fix the leak.

Step 1. Confirm the Leak

In the summer, swimming pools can lose up to 2 inches of water per day through evaporation alone, so it’s worth ruling that out first.

The best way to confirm a pool leak? Do the bucket test.

You’ll need the following:

• A bucket or some kind of large container
• Some sticky tape or a marker
• A little patience

1. Fill a Bucket with Pool Water

Take a bucket and fill it with water from your pool. Get it nice and full, around 1-2 inches from the top of the rim.

The goal here is to mimic the conditions of your pool inside the bucket, which means you must use water directly from your pool. Using water from the tap will not give you an accurate test.

On that same note, filling towards the top of the bucket will give it the same level of sun and wind exposure as your pool, which allows for a more similar rate of evaporation.

2. Place the Bucket in Your Pool

Put your filled bucket on the first step of your pool so roughly the bottom half is submerged.

If your bucket begins to float or move, you can weigh it down by adding a rock or other heavy object to the bucket.

Next, use a marker or some tape to mark the water level on both the inside and outside of the bucket, as this will allow you to compare the amount of water lost in each.

3. Wait at Least 24 Hours

Turn off your pump, filter, and any water features so the pool water remains undisturbed during the test. If you’re using an auto-filler, this should also be turned off.

Wait 24-48 hours for your pool to lose a good amount of water, and keep any swimmers or animals away from pool throughout this period. The longer you wait, the more reliable the result will be.

Unfortunately, if it rains, you will need to restart the test.

4. Check the Results

Here’s the moment of truth.

Looking at your markings, did the water drop roughly the same amount in both the pool and bucket? If so, you don’t have a leak; it’s just evaporation or possibly even splashout.

If your pool’s water level dropped considerably more than bucket’s water level (at least half an inch more, ideally), it’s very likely you have a leak and you’ll now want to figure out where it is.

Step 2. Identify the Source of the Leak

Once you know you have a leak, the next challenge is finding it.

Most pool leaks occur somewhere in the pressure or suction lines, but it can sometimes be a structural leak such as a crack in your pool shell, a tear in your vinyl liner, or even just a bad gasket.

Fortunately, you can narrow this down through process of elimination, by plugging each area of your pool and repeating the bucket test until the leak is contained—at which point you can identify the general region of the leak.

You’ll need the following:

• A pack of o-ring plugs
• Your swimwear (potentially)
• A screwdriver (potentially)
• Even more patience

1. Plug Your Return Lines

To isolate your return line for leaks, you need to prevent any water from going through your return jets.

This involves removing the eyeball fittings from each of your return jets and replacing them with 1.5-inch o-ring plugs. Ensure no return jet is missed and all are screwed hand-tight.

2. Repeat the Bucket Test

Now, simply carry out the bucket test from step 1. Refill the bucket with water from your pool and mark it the same way.

If you come back after 24-48 hours and the drop in water level is more or less the same, you’ve identified that your leak is somewhere in the return line. At this point, you can try fixing the issue unless you suspect multiple leaks.

If the pool still has a bigger drop in water level compared to the bucket, you’ve identified that your leak is NOT in the return line.

3. Plug Your Suction Lines

Just like before, to isolate your suction line for leaks, you need to prevent water from entering your skimmer.

Your main drain is technically part of your suction line but it’s worth doing this separately so you can more accurately locate the source of the leak. We’ll tackle that in a later step.

You can remove the o-ring plugs from your return jets and use them to plug the skimmers around the pool. Again, ensure no skimmer is missed and each one is screwed hand-tight.

4. Repeat the Bucket Test Again

Repeat the bucket test just like the previous two times.

If the water level is now dropping at about the same rate, you’ve identified that your leak is in the skimmer. At this point, you can move to fixing the issue unless you suspect multiple leaks.

If, after the test, the pool is still losing more water than the bucket, you’ve identified the leak is also NOT in the skimmers.

5. Plug Your Main Drain

After ruling out your return jets and skimmers for leaks, the next logical step is to isolate your main drain.

Again, you’ll need to use one of those same o-ring plugs on your main drain, and this will require swimming down, removing the screws on the drain housing, and hand-screwing in the o-ring plug.

Some newer pool drains won’t fit an o-ring plug, so you may need to use an expandable plug like this one instead.

6. Repeat the Bucket Test a Final Time

You know the drill.

If both your pool and the bucket lose the same amount of water, you’ve discovered a leak in the main drain and should now look at fixing the issue unless you suspect multiple leaks.

If your pool and the bucket are still losing water at a different rate, the leak is still present and you’ve now completely ruled out the return and suction lines as the source of the problem.

7. Check for Structural Damage

At this point, you can be fairly certain you have a structural leak since it doesn’t occur in the pressure or suction side of your pool.

You’ll need to check your pool over thoroughly for:

• Cracks in the pool shell (concrete or fiberglass pools)
• Tears or holes in the liner (vinyl pools)
• Cracks in the light line (all inground pools)
• Damage to the hydrostatic valve (concrete or fiberglass pools)
• Cracks in the skimmer itself (all inground pools)
• Loose fittings or gaskets (all inground pools)

If you’re having trouble finding structural damage in your pool, I recommend using the dye test.

Step 3. Fix the Leak

Now that you’ve confirmed the leak along with the general region of your pool, the last step is to pinpoint the leak and repair it.

How to Fix a Pressure Leak

Fixing a leak in your pressure (return) line is difficult without professional equipment and expertise, and is not something I would recommend as a DIY project.

These pipes run fairly deep underground and finding the exact position of the damage often requires precise pressure testing and sometimes the use of specialized sonar technology.

Unless you feel comfortable digging up large areas of your pool, it’s best to call in the professionals for this one.

How to Fix a Suction Leak (Skimmer Line)

Suction leaks can be more forgiving and can sometimes be fixed yourself depending on your DIY skills and the exact location of the leak.

If you’ve identified the leak is in your skimmer line, you can work through the steps below until you pinpoint the source of the leak:

1. Start at the pump and check the skimmer line connection.
2. Follow and inspect the line as it runs through any manifolds, junction boxes, or other plumbing components.
3. Once the skimmer line goes underground, carefully dig up the soil until you find the leak or reach the edge of your pool deck.
4. If you’re comfortable doing so, carefully dig under/through your pool deck and inspect the line up until the very end, where it connects to your skimmer.
5. Check the skimmer line connection to your skimmer.

How to Fix a Suction Leak (Drain Line)

If you’ve identified the leak is in your drain line, there is a limit to how much of this line you can reasonably check yourself.

In this case, you can follow steps 1-4 exactly as above because the skimmer line and main drain line run parallel, except the drain line will divert deeper underground as you get closer to the pool.

The good news is, a pool can operate without a main drain, so you can simply plug it (see previous section) and wait until it becomes more convenient or affordable to make the repair.

However, if no leaks are found between the pool deck and the pump, it’s probably between the pool deck and the skimmer. This may be considerably more complicated to reach without specialized tools.

How to Fix a Crack in the Shell

Moving on to structural leaks, repairing a crack in a concrete or fiberglass pool is usually pretty straightforward and inexpensive.

The easiest way is using 2-part pool putty on the crack, and it can even be applied underwater so no draining is required. This is sold as a temporary fix but can hold for many years and be reapplied when needed.

However, if the putty doesn’t hold or you want a more permanent fix, it will require draining the pool, cutting the crack out, and using a stronger sealing solution. Unfortunately, this tends to be a job best left to the pros.

How to Fix a Tear in the Vinyl Liner

If you have a vinyl pool, small tears or holes in your liner can be repaired easily and cheaply using a vinyl patch kit.

The idea is to glue the clear vinyl liner patch to the damaged area of your liner—which can be done underwater, since the adhesive is waterproof—and then wait 24 hours for it to bond.

Everything you need is supplied in the kit, but if you can get a hold of a sample of your existing liner, using this in place of the clear vinyl patch will be stronger and less noticeable.

How to Fix Cracks in the Skimmer

If you need a quick temporary fix, you can use 2-part pool putty to patch up most skimmer cracks.

For a more permanent fix, though, you’ll want to use Schmear pellets with a solvent like methyl ethyl ketone (MEK), like so:

1. Plug your skimmer to keep it dry throughout this process and prevent the paste from entering your skimmer line.
2. Once dry, apply MEK to a dry cloth and thoroughly wipe down the damaged area of your skimmer to clean it.
3. Use some sandpaper on the crack to roughen the surface. This will allow for a much stronger bond when applying the schmear paste.
4. Follow the steps provided by Schmear, mixing pellets with the recommended amount of MEK to create a thick-ish paste, and then applying it over the skimmer crack.
5. Allow 24 hours for the paste to cure and harden before removing the skimmer plug and exposing it to water.

How to Fix a Leak in the Hydrostatic Valve

Most concrete and fiberglass pools have a hydrostatic relief valve, which can be found directly inside the main drain.

This valve is designed to open when the water pressure below the pool becomes greater than inside the pool, preventing your pool shell from “popping” out of the ground.

Even a seemingly small issue with this valve can allow water to leak out of your pool, so you’ll want to do the following:

1. Check for and remove any dirt and fine debris under the opening of the valve that may be preventing a tight seal.
2. Check for a worn or damaged o-ring inside the opening of the valve.
3. Check the spring for rust or other damage that might be stopping the valve from closing.

If the leak persists after following the steps above, your hydrostatic valve probably needs replacing. This is typically done every 5-7 years.

Hydrostatic valves should only be removed and replaced when the pool is drained, and even then you should check the water table before draining to ensure your pool doesn’t pop out of the ground.

How to Fix a Leak in the Light Line

A leak in your light line (the pipe that runs behind your light and goes directly to your junction box) is considered structural because it isn’t connected to either the pressure or suction side.

Since the light line isn’t part of your filtration system, you can fix the leak by simply blocking your water’s access to this line. In fact, some pool construction companies seal this line during the build to prevent future leaks.

You can do this using a 3/4-inch rubber cord stopper, following the steps below:

1. Remove the bulb from the light fixture.
2. Wrap the cord stopper around the light cord.
3. Wedge the cord stopper back into the cord opening, tight enough to prevent any water from seeping through.

This method doesn’t require draining the pool, but you may need to replace the cord stopper after a few years. It’s still only rubber, after all.

How to Fix Fittings and Gaskets

If you suspect a bad fitting or gasket is causing your leak, you’ll need to get your swim goggles on and inspect your pool components.

Specifically, you should check for loose or worn fittings/gaskets around your skimmers, drains, return jets, light fixtures, and even the seal around your pool steps if you have a vinyl pool.

Again, turning off the pool and using the dye test can help if you’re struggling to pinpoint the exact area of the leak. As far as pool leaks go, however, this is probably the least common type.

Bottom Line

The bucket test is often the best way to confirm a leak and rule out evaporation. The same test can also be used to isolate the suction side from the pressure side of your pool, and identify the general region of the leak.

The absence of a leak in your plumbing points to a structural leak. Finding a leak in your pool structure tends to be a more tedious job, but careful inspecting and perhaps a little dye will help to narrow it down.

In any case, fixing an inground pool leak is often possible at home, using a mix of DIY methods and products. However, some cases will require the expertise and equipment of industry professionals.