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! — 54 Comments

  1. My gunite pool is leaking. The pool cover has been sucked in and the water is leaking down the hill behind the pool house. A giant stream. Did our pool company fail to winterize it properly? Do we have burst pipes? Thank you for any advice.

    • Hi Amy, so sorry to hear about this! Gunite pools do not normally leak thru the shell suddenly, so I would suspect a pipe leak or pool light leak as first guess. Pool lights are not commonly winterized, and they don’t normally form ‘giant streams’ of water, and only leak down to the pool light level, thru the light cord conduit. Main drains are normally winterized, by blowing air thru the pipe to force out all of the water, and then quickly closing the valve on the air filled line, to keep pool water from re-rentering the main drain pipe, like a finger on the end of a straw. However, there are all sorts of main drain plumbing configurations and many types of valves, so that method may not be always reliable.

      If your water level is very low, to the shallow end floor, below all of the other pipes (skimmer, returns), then it likely would be a main drain pipe breakage. Possibly freeze damage, but also possibly breakage from frost heave of the ground. In most cases freeze damage will spider web crack a pipe along long distances, but frost heave is more of a clean break of the pipe in one spot. It could also be a leaking hydrostat relief valve, some are spring load, and seal with a small o-ring, which can sometimes come out of the groove during vigorous blowing of the main drain. these are located in the main drain pot.

  2. Hi Davey, this is the second year in a row that our above ground Pool empties “for no reason”. We had the liner replaced last summer and the summer before that as well. It’s hard to tell if we lost water this past summer after the liner was replaced because I would fill it routinely when the water was low (I thought it was due to evaporation or the kids splashing around). I did have a harder time than usual balancing and maintaining the pool this summer. When we did close it, around late Sept-early October, we did not see any problems. Slowly, by mid to end of November I noticed the water level going down. Now that all the snow has melted I was able to get a good look and noticed that there is hardly any water in it, just what has frozen over due to the extreme cold weather we had last week. We’ve taken water off of the cover since Oct but not enough to lower it that much and that fast. I’ve seen posts stating that the main drain should be checked but I don’t see a main drain on my Pool. I don’t even see an opening inside the Pool that would give access to a main drain either. Am I missing something? Replacing the liner each year costs almost $1000 each time and does not seem like an appropriate solution. My theory is that the foundation where the pool is was not prepped correctly and therefore not stable and the water may be leaking through the seams of the liner into the ground around the Pool. For now I am going to add more water into the pool so the liner does not collapse and hope that I can find a solution to this problem ASAP. Any suggestions or assistance from you, or anyone, would really be appreciated.

    • Hi Alexandra, sorry to hear about this trouble! For splashout and evaporation, in hot temps for sunny/windy pools, it can be up to 1/4″ per day, or about 1.75″ per week – more than that and I start to suspect a leak. Aboveground pools don’t have main drains, as they don’t usually have a deep end. Main drains (2 are now required) are used at the deepest spot of the deep end, almost exclusively on inground pools. Some A/G pools have what I call a LWS, or low water suction port, on the wall about 1/2 way down the wall, as a second pool outlet (in addition to the skimmer) to bring water to the pump. And of course A/G pools also have 1 or 2 wall returns, where the filtered water re-enters the pool. A/G don’t usually have thru-wall lights, but can. A/g pool leaks are thus usually easier to find, because the pipes (hoses) are exposed, and equipment drains down easily, and there are very few ‘incursions’ or holes cut in the liner, as potential leak sources. In your case, you will likely find a leak in the liner, at the level that the water is currently frozen at, or around there. When it thaws, put on waders and walk around slowly, inspecting the wall, at the water level. Larger holes may have debris stuck in them, a telltale sign. Smaller pinholes are harder to spot. Look closely at the skimmer area, where the wall panels normally join together, and may have sharp edges or screw heads. If your pool is completely empty, or has only a few inches of water, then the floor and intersection of wall/floor is your prime area. Find the hole(s) and patch the liner, probably no need for a new liner. If the foundation beneath is rough, with pebbles or rocks, that can cut the liner, under the weight of the water. You may have noticed that while swimming however, if the floor was not smooth. Adding more water is a good idea, to keep the liner from shrinking in the cold weather. See if you notice more moisture in the soil areas around the pool, that may provide a clue. If all of your plumbing lines are plugged, and the water level is below any such incursion anyway, and you didn’t pump out water with your cover pump, the liner likely has a hole, or possibly a failed seam, although that is more rare. Good Luck and hopes for a quick fix!

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