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Your pool will naturally lose some water to evaporation, some to splash-out and some to backwash wastewater. You will also gain water from rainfall. My rule of thumb is that if you're routinely adding more than two inches of water to your pool per week, you probably have a leak that is worth spending some time and possibly money to repair.
Pools are meant to be watertight but sealants will deteriorate while other parts of your pool shift and settle or just plain wear out. Pools can leak through any of the fittings or accessories, plumbing, or even right through the shell. It is important to repair leaks, not only to save water, heat, and chemicals, but also to prevent undermining pool structural components and washing away fill dirt that supports the pool walls and pool deck.
Leak detection is a highly specialized branch of the industry. Ninety five percent of all phone calls I get from worried pool owners about a leak turn out to be inexpensive to repair. So relax, if you can't take care of the problem yourself a professional will be equipped to do so for you. If you suspect a leak, review the following things before calling for service:
This may indicate a pressure-side return leak. With the filter pump on, the plumbing on the pressure side (after the pump) is under pressure. This can open up small drips into spraying gushers. Check the waste or backwash line for water consistently running. One inch of your pool water can equal 500 gallons. Check downhill from a pool, looking for weepers where underground leakage is surfacing. Check for soft or wet spots in the yard, on the side of the pool where the plumbing returns water to the pool.
This usually indicates a suction-side leak, or on the pipes that bring water from the pool. With the filter pump on, the plumbing on the suction side is under vacuum. Air can be drawn in through otherwise leaking voids. You may notice air in the pump basket (if you have a clear lid), air bubbling out of the return lines, or air repeatedly built up inside the filter tank. Use tape or a pencil to mark water levels.
This does not rule out leaks in the plumbing, but turns a suspicious eye on the shell of the pool, looking for cracks in the plaster or tears in the vinyl. Look closely at the tile line and look real closely inside of the skimmer(s). The most common leak we fix is a separation between the plastic skimmer and the concrete pool. This is easily fixed with some pool putty. If you see something that looks like a crack, drop some test dye near it with the pump shut off and water still to see if the dye is sucked into the crack. Under water lights can and do leak as well, especially the conduit that runs from the light niche to the junction box. Filling the opening of the conduit in the back of the light niche with pool putty, black butyl tape, or using a cord stopper are ways to fix this problem.
Look closely at the filter, pump, heater, and valves. Check the ground for moisture. Turn the pump on and off looking closely for spraying water when the pump is turned off. A small drip or two will not be the source of the leak. If loss of water level is noticeable in the pool, it won’t be a drip, but a trickle at least.
You may be able to close the skimmer valve and allow the water level to drop below the skimmer, running the pump on the main drain. If the water continues to drop, we can rule out the skimmer (although there can always be more than one leak).
When the water stabilizes at any specific level, dye test and inspect around the pool very carefully, at that level. Look for small debris which may have been sucked into the crack or void. This is a good indication of a leak. If the water stops at a wall fitting, wall step, or pool light, give it a good close look. Shutting off the pump, and plugging the drain, skimmer and return lines with expansion plugs, is another test, to rule out the plumbing.
Take a walk outside the pool deck and between the pool and the equipment pad. Check for wet soil and eroded areas. If your pool has a downhill slope near the pool, walk down the hill to see if you can notice water weeping from the hillside – at least you know where it’s going!
If so, there are special considerations. Look for sinkholes where sand under the liner may have washed away. Look for tears or separations around all fittings: skimmer, returns, cleaner line, steps, pool lights, main drain etc. Pay close attention to steps and corners, where the liner may be stretched more than normal. If an animal had the misfortune to fall into your pool you may notice claw marks (tears) just below the water line. Spending time under water with a mask may be required to find a small leak in a vinyl liner. When pool liners become old they may develop pinhole leaks easily.
There can always be more than one leak, but most of the time, it’s a gash in the liner, about 1” long, which can be easily repaired with a vinyl patch kit, or with clear vinyl sealant. I have successfully (though not beautifully) patched liners with gashes as long as 18” before. You can use clear vinyl patch material, which tends to yellow over time, or use a piece of liner sample, or the skimmer / drain / step / light cut-outs, from when the liner was installed. Or use the EZ Patch 28 clear sealer, or Anderson Flexible Sealer, which are gels squeezed from a tube, and smoothed over the area with your fingers.
You can do the “bucket test” on your pool to measure evaporation. Place a bucket of water beside the pool and mark both the water in the bucket and the pool water level. Wait 24 hours then check the loss of both. If the pool loses more water than the bucket, then you have a leak.
Most pool leaks are not in the underground plumbing, although it’s every pool owner’s worst fear, a large backhoe coming in and ripping up the pool deck. It does happen occasionally, that a leak occurs at a pipe connector under the pool deck, or beneath the skimmer, but repair rarely involves a backhoe.
To determine if the pipes are leaking, the simple way is to shut off the pump and plug all the lines. If it keeps leaking, we know it’s not the pipes. If it stops leaking, the plugs can be removed individually to see when leaking continues, although some pools only leak with the pump running. Once narrowed down, a pool plumbing pressure test can be performed on the underground plumbing pipes, to see which ones are leaking.
A pressure testing rig or stick is used to test individual lines, to see that they hold pressure. Experts can also introduce air into the pipe, and with headphones and a giant ‘stethoscope’, listen for the sound of escaping air from an underground leak. In this way, they are able to literally draw an “X” on the deck, or in the yard – ‘dig here’.
In most cases, a small 3’x3’ hole can be cut into the deck, to repair the break. Very rarely does the entire run of pipe need to be replaced, and if it did, it would likely be abandoned, and a new pipe run in its place.
For concrete pools with the traditional perimeter tile band at the waterline, leaking is most often found inside the skimmer. In rare cases where the pool bond beam cracks behind the tile, and also cracks the tile, pools can leak water through a crack in the top of the pool wall. Cracks in pool tile can be cleaned, dried and filled with EZ Patch 22.
For concrete pools with surface cracking, most of these don’t leak, especially the smaller surface check cracks or shrinkage cracks on steps. But for larger and deeper cracks, these definitely can leak, and can be dye tested to verify. Cracks can be filled with pool putty, silicone or plaster mix to seal most small cracks. Large cracks running across the pool or down the walls will need more prep and a two stage repair of injected sealant, followed by a finish coat of plaster mix.
Nearly all inground concrete pools will develop leaking problems at the skimmer throat at some point. Expansion and contraction of the pool and deck moves the skimmer slightly, breaking the cementitious seal between the pool wall and the skimmer. The seal is on both sides and the bottom of the front of the skimmer, and can be dye tested (with pump off), to determine if water is being drawn into cracks around the front edge of the skimmer opening. Pool Putty is often used as a temporary repair to seal up leaking concrete skimmers. For a more permanent repair, chip out the plaster and replace with EZ Patch 1.
Vinyl pool skimmers can also begin to leak water where they seal up to the wall. Use a large #3 Philips head screwdriver to tighten all screws around the skimmer faceplate, very tightly. Replace the skimmer gaskets for the skimmer faceplate if leaking continues. Dye testing can be used around vinyl skimmer faceplates to verify leaking (with the pump off).