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How to Find and Fix a Pool Leak in 3 Easy Steps

If you notice the water level in your pool dropping faster than usual, you may wonder if there's a leak. If you notice wet areas around the pool or near the equipment pad, it's definitely time to start troubleshooting. It’s not too difficult to find most pool leaks with a little know-how and the right leak detection tools. Once you’ve found the source of water loss, you can make many simple pool leak repairs yourself. In this blog post, we’ll walk you through the three easy steps in the pool leak repair process:

dropping water levels can indicate a pool leak

1. Recognize the Signs of a Pool Leak

pool leak detection

2. Pinpoint the Exact Location of the Leak

repair a pool leak

3. Fix the Pool Leak

Step 1: Recognize the Signs of a Pool Leak

The first step is simply identifying that a leak exists. Pool leaks often start out as a minor, occasional drip. But they can progress into a much larger issue if not addressed quickly.

A leaky pool costs money with every drop, wasting perfectly good filtered, treated, and sometimes even heated water. But they stand to cost you more than just water, chemical, and energy expenses. Low water levels may also cause the pump motor to overheat. Leaks under the equipment pad or pool deck can cause concrete slabs to shift and crack. If you own a vinyl pool, the liner may begin to pucker and pull away from the wall. To prevent these costly damages, keep a close eye on the pool so you can recognize the signs of a pool leak right away.

While you’re in the diagnostic stage, be mindful of water loss caused by evaporation, backwashing, or splashout. Also figure in water gain from natural sources like rain. If you do suspect a leak somewhere, be sure to turn off any auto-fill or water leveling devices while you’re identifying and repairing the pool leak.

BONUS TIP: Leaks aren’t just an inground pool problem. Above ground pool leaks can soften supporting soils around the edge of the pool, causing the floor and walls to shift, wrinkle, or fail. Prolonged exposure to wet soils may even cause rust and corrosion to steel pool walls and supports.

Wet Areas Around the Pool or Equipment Pad

Take a slow walk around the outside of the pool, looking for moist areas or standing water. Further away, especially downhill from the pool, is there any running water? If you know which side of the pool has the underground plumbing, this can be helpful. However, let me put your mind at ease – a pool leak is almost never in the underground pipes. Unless the ground has shifted significantly, or you suffered a particularly harsh winter and didn’t winterize your pool correctly, the leak is likely elsewhere. The most common underground leaks are usually underneath the equipment pad (where the pipes run vertical) or near the skimmer, drain, or return pipes.

Next, check the equipment pad where the pump and filter are located. Again, look for wet areas, erosion, or standing water. Take note of any drips coming from equipment and pipes. Just remember, if you’re losing a significant amount of water (several gallons per hour), the main source of the leak is likely elsewhere. Slow drips above ground still need to be addressed. However, these drips not likely to be the cause of major water loss. That said, there is one leak at the equipment pad that could cause a noticeable loss of water. On D.E. or sand filters (not cartridge filters), a backwash valve with a damaged gasket can leak water into the backwash line or hose, even after the valve is returned to the filter position. If water trickles out of the backwash hose while in filter mode, it’s time to fix or replace the valve.

Rule Out Evaporation

In particularly hot weather, a pool can lose upwards of 1.5” to 2” of water per week to evaporation. The rate of evaporation depends on sun exposure, humidity, and wind speeds. To determine if the water loss is actually a leak or just evaporation, do the bucket test. You can use a Mini Bucket Test, or run your own test using a clean 5-gallon bucket.

Avoid performing the bucket test during inclement weather or periods of strong winds, as this can skew the results. Also turn off any auto-fill devices so you’re not adding more water to the pool during testing.

Start by setting your testing container on a pool step. Next, fill it with enough water so that the level on the inside exactly matches the level on the outside. If you want, you can mark the water level on the container with either a marker or a piece of tape. Check back in a day or two to see how the levels changed. If the water level in the container is higher than the level outside of the container, you definitely have a pool leak. But if the water levels match each other, you only have evaporation. Here's a little better explanation of the process using the Mini Bucket Test:

If the bucket test indicates a leak, you can repeat this test a couple more times in the next step. This may help you gain context and determine the general location of a leak.

Step 2: Pinpoint the Exact Location of the Leak

Once you’ve confirmed that a pool leak exists, it’s time to determine where it’s at. Start with general troubleshooting, and work your way down to the exact location.

Common Pool Leaks

While you’re troubleshooting to find the approximate location of the pool leak, keep these common leak sources in mind.

Skimmer Leaks

For vinyl pools, a skimmer is held in place with two gaskets, a faceplate, and about a dozen screws. For concrete pools, the skimmer is encased in concrete and parged with plaster. Because the plastic skimmer will flex and expand differently than the surrounding concrete, leaks at the skimmer/pool interface are common. Look for cracking around the skimmer entrance, and for those telltale tiny bits of debris sucked into the cracks.

Pool Liner Leaks

A pool liner can leak in almost any location. However, the most common vinyl liner leaks occur in areas that are stretched (walls, corners and steps) or areas that are gasketed (skimmers, returns, lights, steps). If you’ve plugged all the lines, and the pool still leaks, check that all faceplate screws are (very) tight. Also inspect the liner underwater, using goggles or a snorkel mask, to see if you can spot any damage or openings.

Pool Light Leaks

Because the light cord conduit on underwater lighting is not winterized, the conduit may crack and leak water. This can also happen because of shifting soils. Pool light leaks are not easy to detect, and cannot be dye tested effectively. However, if you notice that your water level drops to the top of the light and stabilizes, it’s a good indicator that this is the problem.

Pool Plumbing Leaks

Underground pipes can leak. But as we mentioned earlier, this is rare, and your underground pool plumbing is usually not the source of the leak. The most common leaks in pool pipes are just beneath the equipment pad, where the pipes turn vertical. Pipes may also detach directly beneath the skimmer, drain, or return pipes due to significant ground or soil movements. 

Noticeable Water Loss During Specific Times

Does the pool leak even when the pump is off? Or does it happen only while the pump is running? These questions may seem very general, but they can point you in the right direction.

If the pool leaks mostly when the pump is running, you may have a leak in the filter valve (sand or D.E.) that leads to the backwash line or the return lines (cracks expand under pressure). If it only leaks when the pump is off, this could indicate a leak in the suction lines (skimmer, main drain). In this case, you may also notice air coming into the pump basket. Those same cracks that draw air under vacuum will leak water once the pump stops running and the pressure releases. Now, if the pool leaks all the time, this could indicate that the leak is in the pool shell, not the plumbing. Just remember that a pool can have more than one leak!

To rule out plumbing leaks, the next step is to turn off the pump at the breaker, and plug all of the skimmers and returns. For pools that winterize, you may already have plugs that will fit. If not, buy the correct size plugs to fit your skimmer(s) and returns. The main drain is not usually plugged due to difficulty. Remember to leave the pump OFF while the plugs are installed!

If the leak continues while the pipes are plugged, you can assume that the leak is likely in the shell, possibly around the face of the skimmer or an underwater pool light. For vinyl pools, check that all faceplates are tight, and dye test any suspected leaks in the gaskets or vinyl liner. 

Water Levels Stabilize or the Pool Stops Leaking

Have you let the water drop to a level where it seems to stabilize? Many don’t, for fear of letting the water level fall below the skimmer while the pump is running. But if you suspect that the leak is happening in the skimmer or pool lights, this test will help confirm.

IMPORTANT: If you suspect that the leak is deeper than 12-18", or if the water leakage shows no sign of stopping at that level, abandon this test immediately. Refill the pool to appropriate levels, and continue troubleshooting with other methods or consult a professional. Allowing the pool to drain too much may damage the pool structure or your vinyl liner.

If you have separate main drain and skimmer lines in front of the pump, close the skimmer valves, and keep the main drain valve open. Older valves may leak air, so it may also be necessary to plug the skimmers, to keep air out of the pump. If you don’t have a separate valve for the drain, it may be possible to use a vacuum hose connected to the skimmer (tightly) with a hose adapter. Another route is to balance and super-chlorinate the pool, then just turn off the pump for a few days. Use this method if you don’t have a main drain line.

Dye Testing to Pinpoint a Leak

If you need help finding the exact location of a leak, or if you’re just looking to confirm your assumptions, a dye test is the way to go. First, turn off the pump and any autofill devices so that the water is still. Grab a pair of goggles or a snorkel mask so you can see well underwater.

Next, apply a very small amount of dye right up next to where you suspect the leak may be. If you notice that the dye gets sucked in, you’ve just confirmed the leak location, and you’re ready to move on to the next step. A common misconception is that you can just squirt a plume of dye in the general area to determine the leak location, but that’s simply not accurate. The point where you apply the dye needs to be right up against the suspected leak, within 1/4" or less.

Here's a video from Anderson Manufacturing Co. Inc. that shows you how to use their LeakMaster Dye Test:

Advanced Leak Detection

Simple troubleshooting methods leaving you stumped? You may need to use advanced pool leak detection methods. A professional will be able to quickly and accurately diagnose your pool leak issue(s) using advanced methods and tools. They’ll also be able to help you with repairs or next step recommendations.

If you suspect an underground leak, pressure testing the plumbing can help narrow down its location. Individual pipes are pressurized with water and/or air to determine which sections of underground plumbing are leaking (if any). With the addition of air and listening devices, leak detection professionals are able to pinpoint leaks and draw a literal “X” on the ground.

Anderson Manufacturing Co. Inc. has a patented electronic leak finder that detects stray voltage leaving the pool shell. This is extremely helpful for pinpointing leaks in vinyl pool liner pools. Since the purchase price of this LeakTrac technology is on the higher side, it’s used almost exclusively by leak detection professionals.

Step 3: Fix the Pool Leak

Simple Pool Leak Repairs

Most pool leaks are easy to fix once found. Simple repairs usually involve a bit of pool putty, waterproof silicone, a vinyl patch, or a plaster patch. Very small plumbing leaks can sometimes be patched with Pentair Stop Leak, but this shouldn’t be considered a solution for major plumbing leaks.

For leaky pool lights, pack pool putty around the cord where it exits the niche, or squirt a sealant like Underwater Magic into the conduit.

If the leak is caused by a faulty gasket, bad o-rings, or cracked parts, you may be able to find replacement parts online. Skimmer gaskets and filter valve components are some of the most common pool parts needed for a leak repair.

If the leak is caused by a structural crack in the concrete or plaster, you may be able to fix the crack on your own with a bit of Leslie's Patch-It. We have some helpful DIY patching tips in our Pool Plaster Repair blog post.

Complex Pool Leak Repairs

For the most difficult pool leak repairs, a portion of the deck may need to be cut open. Or, in the case of cracks behind the tile line, the coping and tile may need to be replaced to allow for beam repairs.

When extensive freeze damage or old age causes major leaks in underground plumbing lines, an underground pipe may be abandoned, and it may or may not be replaced. A professional will be able to guide you on the best options for your budget and the long term health of your pool. For vinyl pool owners, you may need to buy a new pool liner in order to fix a leak correctly.

Recommended Products

Mini Bucket Test - Pool Leak Detector

Bucket Test

Leak Master - Filled Flourescent Dye Tester

Leak Dye

Rezolin - A+B Epoxy Coating 14 oz White

Epoxy Putty

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Leslie’s makes every effort to provide accurate recommendations based upon current ANSI/APSP/ICC-5 2011 (R2022) standards, but codes and regulations change, and Leslie’s assumes no liability for any omissions or errors in this article or the outcome of any project. You must always exercise reasonable caution, carefully read the label on all products, follow all product directions, follow any current codes and regulations that may apply, and consult with a licensed professional if in doubt about any procedures. Leslie’s assumes no legal responsibility for your reliance or interpretation of the data contained herein, and makes no representations or warranties of any kind concerning the quality, safety, or suitability of the information, whether express or implied, including, without limitation, any implied warranties of merchantability or fitness for a particular purpose.