My Winterized Pool is Leaking Water!


A frantic pool owner called in earlier this week. “I just looked under my pool cover, and the pool water level is down to the floor! Help?!?”

The call was routed to my desk, and I began a process of elimination, which is winter leak detection, by asking a series of questions:

  1. What type of pool – gunite, vinyl or fiberglass?
  2. What type of cover – water bag, or safety cover?
  3. Was the pool losing water during the season?
  4. Have you ever lost this much water before?
  5. Is the water below the returns and pool lights?


The first question is very important, in that gunite pools rarely leak from the shell, with the exception of around pool skimmers. Vinyl liners can leak from anywhere, from small holes, or wherever the vinyl has been cut, for stairs, returns, pool lights. Both types can leak water through the main drain, but this is not a common area for water loss, except on very old pools, or large pools that use a spring loaded hydrostatic relief valve.

bulge-in-liner from water underneathAll pool types must keep water in the pool – all the time. It protects the surface and keeps the pool from ‘floating’ if enough hydrostatic pressure is beneath the pool. Vinyl pools can float too, when enough water gets underneath the liner.

Liners that leak past the shallow end floor may end up with wrinkles or a damaged pool liner, when refilling the pool. Gunite and Fiberglass pools can actually pop out of the ground, if enough water weight drains out!


The second question is also important, because if you have a safety cover, like we have in the picture above, at least the cover won’t fall in the pool when the water drops this much. However, if a heavy snow load falls on an unsupported safety cover, it will damage the springs and possibly break some straps.

pool-cover-fell-into-poolSolid pool covers with water bags will fall in the pool, slowly slipping in as the water level of the pool drops. This makes it easier to see that there is a problem with the water level, but if something is not done quickly, you risk contaminating the pool if a messy solid cover falls in the pool.

Keep the water level in the pool no lower than about 15 inches from the top of the pool coping. Not enough water in the pool, and solid covers fall in the pool, and safety covers are at risk for damage.

pool cover-pump-on-a frisbeeIf you have a solid pool cover and use a pool cover pump, I’ll have to ask… “is it possible you have been pumping out pool water, through small holes in the pool cover?”. This is more common than you think. To avoid this, place your cover pump on an upside down Frisbee® and position it far away from any known or suspected holes in the pool cover.


Questions 3 and 4 are important to the investigation, establishing any pre-existing conditions or trouble with pool leaks. Often, pool owners aren’t aware that they are losing water during the season, if it’s slow enough and there’s a lot of rain. I’ll usually ask them how much water they add during a typical summer week. If it’s more than 1 or 2 inches – they may have had this leak for some time.


The point at which the water stabilizes is a good area to look for a leak. Be aware that recent rains, or water on top of a solid cover will raise the water level in the pool, so the leak may be below the current water level.

Water level stains (bathtub ring), or debris found stuck to pool surfaces, may indicate the level or location of the leak. Looking closely around the stabilized level will usually help you pinpoint the leak, checking the pool surface and any exits of the pool, including the returns and pool light.

For more information on pool leak detection, see a related blog post I wrote “Find and Fix Pool Leaks“.

WAIT UNTIL SPRING?filling-the-pool

In most winter pool leaks, the option to drop a hose in the pool and fill it up as needed certainly exists, and may be a better solution than fixing a leak during winter. If you can however, take a look to see if you can’t find and fix it now.

If the pool cover has already fallen in the pool, pull the cover out, clean the pool, and try to find the leak. If you still can’t locate the leak, fill the pool (after cleaning), balance the chemistry, and put the cover back on the pool.

frantic pool ownerReturning to our frantic pool owner who called in for help on his leak – it turned out to be a false alarm. During our time on the phone, the customer mentioned that a month ago, he had to siphon some of the water, because it was too high, “…and now it’s too low!” he told me.

Digging deeper into his siphoning methods, we figured out that he doesn’t have a leak after all – he just over-siphoned the pool!

“Add 10,000 gallons, and call me in the morning” I told him. 🙂

Davy Merino
InTheSwim Blog Editor



My Winterized Pool is Leaking Water! — 22 Comments

  1. Over the winter the main drain in my pool was leaking due to an accessible crack in the pvc drain pipe. I taped the crack (enough to reduce the leak) and filled the pool. With pool now open for the season, I am wondering the best way to temporarily seal the main drain during the repair. There are 12″ rubber mats that go over the drain covers but I thought diving down and temporarily plugging the drain would be more effective. Any thoughts on best solution to seal drain during repair? Thanks.

    • Hi There, yes, diving down there with a screwdriver and mask, remove the drain cover screws. After a few breaths of air, you can plug the pipe with a #10 or #11 tapered expansion plug. The hole is usually on the side of the drain pot. That will stop any water flow from the pool, assuming your break in the line is below water level. Be careful not to turn on the pump with the plug in, unless you are sure enough the plug is large enough that it won’t get sucked in.

      Plugging the main drain is also a way to determine if the main drain is leaking or not, without pressure testing. And, when main drain lines crack, and the cost to repair is prohibitive, some people may plug a main drain line permanently – for this a glued PVC plug would be a better choice. And, if you do abandon the main drain, you will need to take some measures to improve filtration, circulation and/or sanitation, to compensate for the reduced deep end suction into the filter.

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