Leaking Pool: Find and Fix Pool Leaks

inground pool leaksPool leaks can be aggravating, especially when you don’t see any leakage, and don’t know where to start.

How do you know if your pool is leaking? On a hot day, a swimming pool may evaporate up to 1/4″ of pool water, and a good backwash may use up to an inch of your pool water.

Splashout may be a noticeable amount, if you have a lot of pool activity. After accounting for these unavoidable leaks, if you still think your pool is leaking – read on, my friend.

To remove evaporation from the equation, you can perform a bucket test on your pool. Place a 5 gallon bucket on the first step of your pool, in a swimout, or on the top step of your ladder. Fill the bucket half-full of water and mark the water level with a piece of electrical tape on the inside of the bucket. With a second piece of electrical tape, mark the water level of the pool on the outside of the bucket. Avoid backwashing for 24 hours, and compare the two marked measurements.

The water lost from the bucket will only be evaporation, but the water lost from the pool is evaporation, plus (?) any other water loss. If there is a noticeable difference between the two, you can begin to locate the leak in your pool.

How to Find Leaks in your Pool

Leak detection in swimming pools is a step-by-step process of elimination. There are 4 main areas to check; the Pool Shell, the Pool Light, the Pool Plumbing and the Pool Equipment. Let’s dive right in, shall we?

Leaks in your Pool Shell

When I say “Pool Shell”, this includes vinyl liners, fiberglass shells, plaster pools. Vinyl lined pools have the most vulnerabilities in this area, with the potential for small tears in the vinyl, or leaks at the cuts that were purposely made, for the light, steps, skimmer, drain and returns.

Plaster pools can leak through a crack in the shell, most common in the tile line, or through small voids surrounding pipes that come through the wall, or the very common leak at the interface of the plastic skimmer and concrete pool wall.

To find or to rule out leaks in the pool shell, plug all of the plumbing lines – skimmer, main drain, returns. You can use rubber or threaded plugs – the kind used for winterizing. Shut the pump off at the breaker, so it won’t turn on while the lines are plugged. You may also want to shock the pool beforehand, as you might need to have the pump off for a few days, if it keeps dropping.

Many times, if the leak is large enough, it will quickly drop to, and stabilize at the problem area. This may be right at the bottom of the skimmer, or somewhere around the returns or the pool light. If the water level continues to drop with all of the lines plugged, you can probably rule out the underground plumbing (your worst fear). If, however, the leak stops when you plug the pipes and shut off the pump, jump ahead to plumbing and equipment pool leaks.

When it seems that the water level has stabilized (remember that evaporation will continue, and you may need to subtract any rainfall amounts), you can begin to inspect the waterline area closely.

When your pool shell or vinyl liner has a leak, usually you will find small bits of debris that have been sucked into the crack or rip in vinyl. To confirm a leak in a suspected area, use food coloring or a dye syringe to dye test the area. You can also use pH indicator solution, but be careful not to suck any pool water into the bottle which will dilute the reagent.

Dye testing is done with the pump off, to reduce currents. Squirt a small amount of dye near the area to see if it moves towards and gets sucked out of a hole.

Leaks in the Pool Skimmer

One of the most common areas for leaks on an in-ground pool, leaks can occur inside the skimmer pot, or on the sidewalls of the skimmer, usually from winter freeze damage or excessive ground movement. On vinyl pools, the faceplate and gasket are suspect and can be dye tested, as described above. On plaster pools, look inside the skimmer, to the point where the tile meets the front of the plastic skimmer. Inspect for cracks and debris stuck in the cracks. Dye testing will confirm the leak.

pool-puttyCracks in the skimmer body can be repaired with an underwater epoxy mix, commonly sold as Pool Putty. This can also be used on the front 3 sides of the skimmer, where it mates with the concrete pool, or you can chip out all of the cracked material and replace it with a pool plaster mix to seal it up again.

Leaks in the Pool Light

The conduit that carries the light cord from the light niche to the light junction box is not sealed, and can become cracked from shifting grounds or freeze damage. If your pool water level has dropped down below the skimmer, below the returns and has stabilized at the top of the pool light, you probably have a leak in the pool light conduit behind the pool light.

To repair, reach down and remove the screw at 12 o’clock and pull the light out of the light housing, aka light niche. Conduit leaks are hard to dye test effectively, so the common repair is to seal up the opening where the light cord exits the niche and enters into the conduit.

There are 3 ways to seal up a leaking pool light conduit:

  1. With a golf-ball sized chunk of mixed pool putty, create a mound around the cord as it enters the conduit. Push in and seal tightly against the cord. Allow to cure for 2 days before replacing the light into the niche. Can be done underwater with a mask.
  2. With a tube of 100% pure silicone, squirt up into the light conduit and around the end of the conduit to seal up the exit for the water. After a good silicone plug is made, allow to dry for 2 days before replacing the light.
  3. Use a product called a Light Cord Stopper. This is a plug that fits around the cord, and you push it into the conduit where it makes a fast seal. This method is preferred for the reason that if you need to replace the lamp down the road, you won’t have to struggle with removing the putty, or silicone, which is especially difficult to remove from the conduit.

Leaks in your Pool Plumbing

If your pool has not leaked since you plugged all of the plumbing lines, that could indicate a leak in the underground plumbing. The thought of this can conjure up images of a backhoe operator ripping up the pool deck, but it’s never actually that messy, and many times the problem pipe is easily accessible. Indeed, underground plumbing leaks are fairly rare, but they can occur from deep freeze damage or extreme shifting soils.

A process of elimination can also help determine which lines are leaking; Main Drain, Skimmer or Returns. Leave the plug in your main drain and remove the plugs in the skimmers and returns to start up the pump. If it continues to leak, you can unplug the main drain and replug the skimmers to check for skimmer leaks. Unless you have separate return lines or an attached spa, it is difficult to isolate the return line for leak testing by plugging the lines.

Pressure testing individual plumbing lines can be performed to determine which line is leaking. Then, the leak can be pinpointed further with more advanced detection tools, which “listen” for the leaking. A leak detection specialist will then literally draw an “X” on the deck or on the dirt, and tell you to “dig here”. A small 2’x2′ deck section can be cut out, then the dirt removed to expose the pipe so that a repair can be made.

But again, your worst fears will probably not come true. Most pool leaks are in the shell or the equipment and can be easily located and fixed – by you!

Leaks in your Pool Equipment

This one should be pretty obvious to you. In most cases, you will see water running out of your pump, filter, heater or chlorinator. Could be a quick fix or it could require some equipment repair.

One thing it won’t be is something that is slowly drip-drip-dripping. Small drips on the equipment are not noticeable in the pool water level, and amount to a very small amount of water loss.

A leak at the multiport valve can go without notice if a backwash hose is constantly connected to the waste port. At some point, the spider gasket in your filter valve will fail, and after backwashing, water will continue to stream slowly out of the waste port and out the backwash hose. The same problem can occur if you have a push-pull type of slide valve. Missing plunger o-rings will allow water to constantly flow out of the backwash line.

Plugging the backwash line can stop the flow of water while you order the parts for the repair, but don’t make this a permanent solution. Oh, and installing a secondary valve on the waste line? Not a repair I’d be proud of; better to get inside the valve and fix the gasket / o-ring problem.

In most cases, leaking pools are fixed easily. Don’t keep yourself up at night with worst case scenarios, start with the bucket test and proceed through these stages to find your pool leak. If it does turn into an underground plumbing problem, you may need to contact a leak detection expert to help pinpoint the leak – but most pool leaks are not found in the plumbing, but are one of the simpler types mentioned above.

One more thing. Fix your pool leaks – they not only waste treated and heated pool water, but could lead to other problems such as rusted pool walls, or erosion of a sand pool floor or the supporting soil beneath your pool deck.

Happy Hunting!

Davy Merino
InTheSwim Blog Editor


Leaking Pool: Find and Fix Pool Leaks — 9 Comments

  1. My winterized in ground pool had a quick leak after not leaking for the first month being closed down. the water level has stopped at the bottom rim of pool light! I read that if it’s a leak in the light water usually stops at top of niche. I opened and checked for cracks it’s a metal cone so no cracks . My question is with the water level at bottom of light is it most likely in the seal of the light housing ??? Just needs so thoughts on this before begin removing the 10 screws or so and replacing gasket. The water when it did leak out only took about 2weeks to get to this level. Any help or ideas appreciated .ty

    • Hi Katherine, most pool lights leak thru the cord conduit, or the pipe that carries the light cord out of the light niche and to the junction box. The conduit connection hole is usually located in the upper part of the light niche. Since light conduits are not winterized, a very cold winter can cause freeze damage, or sometimes they crack during deck installation or from frost heave of the ground surrounding. These leaks can be fixed by using a Cord Stopper. Now for vinyl liner pools, there is a gasket around the light, between the light niche and the outer ring. These do not normally begin to leak on their own, but can over many years, or if the liner is replaced – the gasket should also be replaced. If the water is leaking through the gasket, often there exists the telltale signs of small debris stuck in and around the void, or hole. You can add an inch of water to the pool and use food coloring, or our leak locating dye, to Dye Test around the light, and watch for the dye leaking out. Niches themselves don’t commonly leak, the steel or copper is usually good for 30-50 years, but a light leak is usually the conduit, or on vinyl pools, the pool light gasket. Now, if you have a vinyl pool, the leak could also be in the vinyl, in another location, but at the same level as the light, could be around the step gasket, if not in the vinyl liner. Hope that helps!

  2. Awesome post! I’ve been looking for some great advice on how to DIY such common leaking and plumbing issues! I look forward reading more post about various plumbing tips and tricks. Thank you!

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  8. In The Swim is the very best company for Pool Supplies…NO ONE has faster shipping or better prices!! I get my order the very next day, here in Ohio. We LOVE In The Swim!!

    But I am VERY disappointed with INTEX Pool Co. Price on pump and filter unit was great but finding parts is very problematic! Even the INTEX website is out of stock for hoses in the middle of the swim season!

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