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    Leak Detection in an Inground Vinyl Pool

    July 18, 2013



    leaking-pool-waterThere are many problems that can occur if you have a leaking pool, so it's best to find and fix pool leaks right away. In an area that requires you to winterize and cover your pool, the loss of water underneath your pool cover can require a new pool liner. If your water leaks down far enough, the liner will shrink with no water in the shallow end of the pool.

    Water leaving the pool can erode supporting soil behind the walls and under the pool deck, or it can erode a sand floor, and even vermiculite floors in some cases. Water up against the walls can rust steel walls over time, and if leaking water has nowhere to go, it can come under the liner, creating bulges beneath your liner.

    The chemical balance will always be off as you will constantly be adding fresh water to keep the pool filled. Both of these can be expensive and in some cases damaging to your pool. Water is not free - especially heated and treated pool water - so you want to find and fix pool leaks when they occur.

    Pools can leak from holes in the liner, underground lines, underground fittings or connections, cracked face plates, torn gaskets, stripped screws on faceplates, walk-in steps, main drains, light niches, and backwash line leaks. These are all pretty common areas for pool leaks.


    leaking-pool-waters Maybe you're not sure if you have a leak, or if it's just hot weather evaporation. You can do what’s called a bucket test. Get a 5 gallon bucket and fill it 2/3  full with water and mark the level of the water inside the bucket with a marker or tape mark, set it on the deck right next to the pool. Mark the water level with a tape mark of the pool water level also. Wait 24 hours and than check both levels to see if the water has gone down. If so, and the level has gone down farther in the pool than in the bucket then you do have a leak. If they both have gone down the same amount, your 'pool leak' is due to evaporation.


    In the Pool, or in the Plumbing? If you have determined that the pool has a leak, the next step is to shut off the pump (remove the trippers from your timeclock, or shut off the pump at the breaker), and plug all of your pool lines to see if you're still losing water. If you are, the leak is in the pool and not in the underground lines or the pump and filter system. If the water does not go down, then it is in the plumbing lines or filter system. If it is the pool itself than you start checking everything in the pool itself, cracked face plates, loose or stripped screws on faceplates, step screws, hairline cracks in fiberglass steps.

    leaking inground poolsDye Testing the Pool. With the pool pump off and the water still, use a small bottle of bright food coloring or an old test kit reagent and slowly put the dye around your light niche and face plates, and anything that looks like a hole in the vinyl liner. do not use fresh test kit reagents, because if you suck water into the bottle, it will dilute the reagent, giving you false water test readings.

    Squirt a small amount of food coloring close to suspected areas, and watch carefully to see if the dye gets sucked in and if so that is your problem area. An underwater mask can be helpful, especially for checking areas deeper under the surface.

    Pool Light Leaks. If it is around your light niche, then remove the light to see if the niche has cracks or holes, and if not the use a cord stopper which is a plug with a hole in the center and a slit so you can wrap it around the cord and plug the hole where the cord exits the niche.

    Face Plate Leaks. If it is a stripped screw on a face plate or step, remove the screw and wrap it with Teflon tape and screw it back in - that is usually enough so it will tighten up and not leak. If you find that it's leaking through a cracked skimmer or return face plate - replace it and the gasket.

    pool-water-leaksPool Liner Leaks. Some holes in a vinyl liner do not leak, but if you find any, it's best to use a vinyl patch kit to seal it up. When inspecting your liner, swim slowly around the pool with a mask and snorkel, and look for anything that looks like a hole. Leaks in a vinyl liner are most common in corners, near steps or swimouts, and faceplates, but can occur nearly anywhere.

    If the leak is a small hole in the liner then the only way to find it is going over the complete pool inch by inch to try to find it. A leak detection company has leak detection tools to find small holes in liners that you would never find, using low voltage electrical testing.


    Leaks in the Plumbing.  It's rare, but if you determine that the leak is in the pool lines you now have to determine which one it is . You can plug off the skimmer and run the pool on the main drain only, or the other way around, in a process of elimination.

    If the pool stops leaking when all of the lines are plugged, you can remove plugs, one by one, from skimmer, main drain and return lines, to see if the leak starts again. With the pump not running, leaks in a return line will slow down, and sometimes stop leaking all together, whereas on a skimmer or main drain line, they may leak more when the pump is off. Sometimes, a skimmer or main drain leak will draw air into the pump, while the pump is running.

    This process of elimination can take many days, so boost up your chlorine level and brush and skim the pool each day to maintain the water quality.

    pool-leaksPressure Testing the Plumbing. Pressure testing can be done with water or an air compressor. This involves isolating one particular plumbing line, by closing a valve or plugging the pipe at one end, and using a test plug on the other end to put the pipe section under pressure, with water and/or air.

    You can hire a professional leak location company, or pool service company to pressure test for you, but you can do it yourself with the right test equipment. Once the line is determined a leak detection expert can usually pinpoint the leak. Geophones are used for this, like a stethoscope - they can hear water running underground. Then, you can literally draw an "X" on the deck, to say "dig here".

    Broken underground pipes are not usually the source of most pool leaks, but if it is - a 3 ft square section of pool deck can be cut out to access the pipe. Not as dramatic as you may think, but if the deck is not very wide, it may be easier to tunnel underneath the deck to expose the pipe, and replace the broken section.

    Leaks in the Equipment. Many pools may have a small drip back by the equipment, or a wet spot on the concrete under the pump. Unless you see LOTS of running water - this is not usually the source of your leak. For an inground pool of 20,000 gallons, an inch of water loss equals several hundred gallons, which is very evident if it's leaking above ground.

    pool-is-leakingLeaking Backwash Line. A very common leak at the equipment pad is a multiport valve that is slowly leaking out of the backwash port. If you leave your backwash hose connected and rolled out all the time, you may not notice the leaking out of the other end of the hose.

    Check this, and if you find water leaking out of the backwash line, the correct repair is not to install a valve on the backwash line! The correct repair would be to either replace the multiport valve, or replace the parts causing the leaking, which is usually the spider gasket or the internal spring.


    My best advice to you is to eliminate the obvious sources of a leak, and if you can't find it contact a leak detection company, with a detailed record of what and how you tested. Most will charge a minimum of $250 - but it can be worth it, saving you a lot of time and testing, and weeks of downtime.

    IF you need to locate a leak detection company in your area, check the yellow pages or do a few online searches for local companies in your area.  

    Larry Weinberg
    SPP Pool Expert

    Blog Author
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