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. ­čÖé

Davy Merino
InTheSwim Blog Editor



My Winterized Pool is Leaking Water! — 32 Comments

  1. Have a brand new above ground pool.the skimmer cover looks like it’s not sealed because I see drops of weather coming out of the skimmer on the out side of the pool .how do I stop it . The water is now almost below the there a way to seal this better?

    • Hi Jackie, aboveground skimmers have 3 gaskets, on on the outside of the pool wall and two on the inside of the pool wall, one under the liner and one on top of the liner. If water is leaking on the outside of the pool wall, the outside gasket is bad, or the screws are loose. Remove the front faceplate by removing the 10 or 12 screws, and then you should see the 4 round head screws that secure the skimmer tightly to the pool wall. Since the pool is new, the gasket is probably good, just the screws are loose. Tighten the up, replace the faceplate and raise the water level to test. If it still leaks, order a set of skimmer gaskets and replace. Check that the wall is not bent at the sealing point, crimps or bends in the steel wall make it harder to make a good seal. Good luck!

  2. I have an above ground pool and patched a leak in the liner floor prior to closing our pool. We plan on replacing the liner in the spring. We mistakenly drained all the water out of the pool at the end of the season and covered it. We had a huge rainstorm over the weekend and the cover caved in and one side of the pool collapsed. My husband was able to fix the wall and reattach the liner. We refilled the pool but overnight half the water has drained out!! What do we do now??

    • Hi beth, if you can swing it now, I would do the new liner now – like this weekend or the next. If not, drain the pool fully and patch up the liner holes again with large heavy patches, or use Anderson Leak Sealer or EZ Patch 28 – which squeeze out of toothpaste style tubes – the previous patch may be leaking or there may be other leaks. Find them all and refill and recover the pool, and that may hold you over winter…

  3. Hey, I have an above ground pool, 15 foot round. I dropped the level below the skimmer when I closed. I looked out today and the water level was about a foot below where it had been when I closed. I had a leak in the one gasket for the inflow, but it’s below that level. None of the ground around the pool is boggy that I can detect (there is an area with a deck that I can’t check). Is it possible it’s evaporated off? It’s been exceptionally warm since I closed and when I checked the water this past weekend it was like opening is a shower stall when I peeled the cover back. Any thoughts?

    • Hi shouldn’t be evaporation, it’s covered, right? If you have been pumping rain water, and there are holes in the cover, you could pump pool water out thru holes (use an upside down frisbee to remedy). Otherwise it could be a leak, and a leak in a winterized above ground pool, below the skimmer, is cause for concern. Concern that the cover will fall in, or tear, or concern that the liner will be ruined, or worst case, that a large ice sheet will form, and the pool will leak out, below the ice sheet, and the ice sheet will slip, fall and damage the pool :-0 So it should be looked into, pull the cover halfway off and inspect the pool return, and any other gasketed holes in the pool. They can be leaking between the vinyl liner and the pool wall, or sometimes drip down the outside of the wall. Then look for any vinyl rips or tears, they sometimes have debris stuck in them, sucked into the tear. Shouldnt be too hard to find on a 15′ round! Hope not…

  4. Hi, I have a 15 x 26 oval OGP with vinyl liner and closed it for the winter with a solid cover. The water level has dropped 3/4″ over 4 days. I can tell this by looking at the skimmer cover. I can see the water level through this semi-transparent skimmer cover and marked it with a Sharpie. I figured this to be about 39 gallons per day.I live in Massachusetts. I have couple questions:
    1.) If I remove the winter cover, do you think there is a good chance I could see the hole at this leak rate?
    2.) If I choose not to remove cover, can I just fill the pool occasionally until it freezes and find the leak in the spring without damaging the pool?

    Thanks for any advice.

    Mark in Massachusetts

    • Hi Mark, i would carefully watch the leak, and see if it stabilizes in another few days. If it continues to drop below the skimmer, several inches, I would remove the cover to try and patch it. The pool won’t freeze solid from top to bottom, so the largest fear :-0 is that a thick ice sheet will form across the top of the water, and then the pool will leak below the ice sheet, and then BOOM! the very heavy 6-8″ ice sheet falls or tilts in such a way as to damage the pool or liner. So, if the leak is up around the skimmer or return, just let it drop to that level and you’ll be fine, or you could pull back the cover and fix it now, your call. But if the leak is on the floor, or lower on the wall, it should be fixed before winter sets in.

  5. We have an above ground pool. A few weeks ago my wife notice it was leaking from somewhere because the ground was wet below the skimmer and the water was lowering. We tried looking for the leak but have not been able to find it. We thought it could be the skimmer so we drained the water below the skimmer to see if it would still keep lowering. We think it could still be leaking because the ground below the skimmer seems to still be wet but the water level doesn’t appear to be dropping. If it is still dropping its doing so very slowly where after about a week we still cant tell if its falling or not. However we can still see that the ground is still wet. Its not wet all around the pool, just at the bottom below the skimmer. Its the end of the season now and we’d like to close the pool, and hopefully next spring figure out where the leak could be from? Not sure if this would be a good idea, or if we need to figure out the leak first. I’m just looking for some advice on what the best way to handle something like this would be? Thanks in advance.

    • Hi Sy;

      The leak very probably is in the gaskets behind the skimmer faceplate. I would order new faceplate and gasket set (2) for your particular skimmer (they are all different), and replace them before closing, fill the pool back up first and test it out. It could also be the liner of course, but it would be a pretty good sized and noticeable hole to lose that much water. Most likely the water is leaking down in between the wall and the liner, and running under the pool wall, making the ground wet outside the pool.

  6. 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.

  7. My in-ground gunite pool was losing practically all water (about 30,000) within 2 months. I have to add water … BUT! Now the opposite happens – the level of water under the cover RISES! We had some rains lately (Eastern PA), so how to explain? Ground waters are getting into the pool? Could not find anything on the web …

    • Hi Val, some pools have an automatic hydrostatic relief valve in the main drain pot, to allow ground water under high pressure, from a high water table, to enter the pool. But only if it’s spring loaded and automatic, other types of hydrostat valves have to be manually opened. Another possibility is that the very high water table is leaking in through a crack in or around the skimmer, or possibly even being sucked into a suction pipe that is cracked underground. Or it’s raining a lot at night, when you don’t notice it? It’s definitely a rare problem to have, so I’m just grasping here for ideas…

  8. Hi, So my 15ft round pool lost all of its water during the winter, I didn’t think there was anything I could do short of continuously putting water in so I just let it drain… I have a idea where the leak is and will be easy to patch since there is only about an inch or so of water in it. My concern is the integrity of the pool since thousands of gallons of water leaked into the ground below. What are your thoughts?

    • Hi Lee, Good question. sometimes when thousands of gallons leak out one side of the pool, the ground softens and slumps, resulting in that area of the pool dropping an inch or so. Good A/G construction practices can prevent it, with french drains and gravel installed to remove such water away from the pool. Lots of ground water around the pool can also rust the bottom ring or bottom portions of the wall, but not a one time event, takes years to breakdown the coatings. You will probably be OK – you’ll know for sure after you refill the pool, and look at the water level on that side of the pool, if it is higher than the rest of the pool, that means the pool has settled a bit. Then, you’d just have to live with it, I suppose.

  9. We have a 18×36 inground pool (vinyl) and checked pool in January everything looked fine checked again then in February water was down to third step. now no water in shallow end

    We’ve had the pool since 1987 never had any trouble. In July of 2015 put new liner in. Help!


    • Hi – yikes! I know this is horrifying, but try not to stress to much. If the water level has dropped below all ‘cuts on purpose’ to the liner (steps, returns, skimmer, light…) then that only leaves the main drain as a possible leaker, or the vinyl liner. That’s good news – you’ve ruled out a lot of mystery. Pull the cover off now, if you haven’t already, and take a good look. You may find a dead animal (!), or maybe a small pump that a helpful spouse hooked up to lower the water level. Barring that, you would next inspect the pool liner, very closely, at or just above the water level. Using an inflatable boat (or wetsuit) may be needed. Look closely for anything that looks like a hole, they often have debris (small grasses) stuck into the hole, being sucked in to the hole. At the rate you describe the leak, it should be visible tear or hole. If you don’t find one, check again, or have a different set of eyes look closely. There may be more than one leak, or hole in the vinyl. Now, if you look closely twice or thrice, and see no hole, then you can assume that it may be the main drain. Could be the pipe, or it could be the gaskets that seal the liner to the main drain. It could also be a leaking hydrostatic relief valve, sometimes placed inside (directly in the bottom center) of the main drain pot. The gaskets and drain ring (the one with 8 screws around it) can be dye tested with food coloring, to see if that is the leak, although clear water is needed – which may require filling and starting the pool, to find and fix the leak. Alternatively, you could just drain the pool and replace the main drain gaskets. If the drain ring is leaking, you may have some recourse with the person who installed the liner, but only if they are super-nice guys. If the pipe is leaking on the main drain, you can plug the line, and close the valve on the other end, and see if the water level holds, and stops leaking. If so, you could a). Try Fix-A-Leak, pressurizing the line to fill the cracks, or b) repair or replace the line, or c). abandon the line, and use a pool cleaner more often to help circulation. But – it’s likely not the pipe (most rare). Most likely the drain or the liner, or a pool light or low water suction line at or just above the stabilized water level. Good Luck – let me know if you have more questions or information to share.

  10. I have a 21 foot round pool and when I closed it it was fine but I didn’t drain the water off the winter cover and my pool water levels dropped about two or two and a half feet deep. I was wondering do you think I have a hole in the liner or is it from all the water pushed over the side cuz there’s air behind the liner I don’t think there’s a hole

    • Yes, your theory sounds correct. When the pool cover fills up with water very deeply, it can force pool water to drizzle over the edge of the pool wall. Or if you have a hole in the pool cover, and when you were pumping off the pool cover, you may have also been pumping out some of the pool water, along with the cover water. Take a good around the edges, and if you don’t see anything that looks like a hole (many times there is debris stuck in the hole), then you’re probably fine. Go ahead and fill up the pool, and if you do discover a leak later, just use some vinyl patch, or Anderson Flexible Sealer

  11. I have a 16×32 inground (vinyl) checked to see how water was doing! NO WATER in the shallow end! Don’t see a rip or tear! What is the best way to find the leak!

    • Hi Joanne – Yikes!

      Let’s pull off the cover completely, if you haven’t already. Carefully enter the pool, wearing some non-skid shoes, and carefully inspect the pool at the water line. First, to see if the water level is at or near a cut in the liner made on purpose – such as steps, returns, lights, etc. If it’s way below anything like that, then inspect closely around the water level in the pool (you can use an inflatable boat, or put on a wet suit). Looking for a hole in the liner that you can patch. Corners or angles in the liner are often the first suspects.

      if there is no hole in the liner, at all. It looks perfect… then, you may consider some other sources. Usually only two, if the pool lines were plugged for winterization. Those two are the main drain and the (possibly) hydrostatic relief valve in the drain pot. The main drain pipe could be broken, but that’s actually pretty rare, so don’t get worried until you know. It could also be the main drain ring, the sealing ring which has a gasket…, or sometimes builders use automatic hydrostatic relief valves, which have an o-ring, and if something is stuck between the cap and o-ring, small stick for instance, then it can leak.

      Another source of such a leak is mistakes made when lowering the pool water level, and overpumping it – for those with mesh safety covers, and the water gets too high. Or, for solid floating pool covers, if there are holes in the cover, and your cover pump is set near the holes, it can pump pool water thru the holes, and out the pump discharge hose, lowering the water level.

  12. I have an above ground pool that leaked last year for the first time just be low the skimmer. So before I opened it last summer I change the gasket behind the skimmer. I thought this would fix the problem but again the pole level is lower. Should I check for leaks in the liner or change the whole plastic skimmer box completely? Thank you for any advice

    • Hi Sean, I assume that your pool is just now being opened. If your pool cover had any small holes in it, your cover pump could have lowered your pool water level, by pumping water thru the holes in hte cover… but assuming not, then I would first inspect closely around the level of the water, before filling, looking for any holes in the vinyl, or any debris stuck in a hole, which gets sucked in there by the water. You can then use food coloring to dye test (might need to add an inch of water first). You can also dye test the skimmer faceplate, and also the return and light rings, if applicable. No need to change the hole skimmer, unless parts are cracked or missing. Skimmer faceplates, by the way – must be tightened Very Tight! Use a large #3 Phillips head to really crank the screws down until you hear the plastic creak. Also, two gaskets should be used, one behind the liner against the wall, and one on top of the liner, underneath the faceplate.

  13. Hi, I have a semi-inground pool with salt-water system. I woke up yesterday to find the pool cover lying in the almost completely empty pool. I think the pool cover siphon drained it overnight when the cover straps tore. My son climbed in to remove the large blocks of ice from the cover and we siphoned off the rest of the water. I added water (almost at the half way mark now) and was able to repair the cover straps. Can I add shock and ph without attaching the pump? I’m not able to take it out of storage without my husband’s help.

    • Hi; yes you can add chemicals without the pump running. Dissolve your ph chemical in a bucket of water, and pour around the edge. Rinse the bucket clean, fill with water again, and then add granular chlorine and dissolve it by stirring for 1 minute. Pour the solution into the pool, being careful not to let undissolved granules fall in as the bucket empties. After adding chemicals, use your pool brush to distribute by creating some circulation with the brush.

  14. We have an inground pool. the saftey cover has dropped into the pool at one section. We cannot get out the pool due to snow levels around the pool to look under it (and I am not sure how we would be able to see anyway). Mid summer we had a leak crew come out and the plugged all the leaks in the pool and the water level remain stable for 2 months till we closed. Now this. There is nothing we can do now till May when we open correct?

    • Hi Beth, Safety covers are not usually affected by water level in the pool, unless the water level drops lower than 18″ from the cover – in such cases, the water level no longer supports the cover, and when wet/heavy snow and ice falls, the weight can bend cover springs, or tear cover straps. In your case, if the water level has dropped to a very low point, you can add water to the pool from a hose, to raise the water level again. If you can remove some of the snow, you can look under the cover, or cup your hands around your face and put your nose right up to the cover and you can see thru a mesh cover, to check water level. It could be possible that the water level is normal, and what you are seeing is the cover stuck to the ice and being pulled/stretched down. Let me know if you have other questions. When the ice thaws enough, pull the cover back tightly over the pool, and if there has been water loss, add water to fill. If it drains again, remove the cover and look around the water line (where the water level stabilizes) for failed patches, obvious holes, or places where you see debris stuck to the liner (stuck in a hole).

  15. I came home yesterday to find our solid inground pool cover had fallen in the pool but more importantly, the water has leaked out SOMEWHERE down to about a few feet in the deep end. We have a vinyl cover that we planned to replace in 2018 but which we thought still had some life in it. My major concern is whether the ground around the pool is safe. Is there a chance for a sink hole or anything since all the water has clearly seeped into the ground? Also, what could have caused this so suddenly and dramatically.

    • Hi; likely no problem with the ground water, no worries there. Two things could have caused this, maybe 3. first is a wild animal that fell in the pool, trashed the cover and ripped the pool liner trying to get out (he may still be in the pool(!). #2 – old liners can sometimes just ‘snap’, because they become so brittle, that they just rip, during one cold day. #3, a pool cover pump, used for solid inground pool covers, could have been placed in an area of the pool cover which had a hole – and then the pump began pumping out pool water, through the hole in the cover, until the pool was so low, that the cover fell in the pool.

  16. Hi, I have an above ground pool, one of the rods popped through the liner making a perfect round role, little like a half dollar, is this fixable, another issue we had a gopher go under the liner about two years ago, should we try to work our his tunnel damage or can that hurt the liner, pool only 4 years old..

    • Hi Kathy, the small hole sounds patchable, with a regular vinyl patch kit. Doing it on both sides of the hole will make it stronger, to prevent further rupture (hopefully!). You can also wrap the rod end with duct tape or something to pad it a little, or cover the sharp edge of the rod. For the gopher tunnels, I assume that you have a sand floor under the vinyl. You can smooth out the edges of the tunnel using a rounded blunt instrument. I like to use a 3-4 ft length of PVC pipe, attached to a 2″ Tee fitting, and use it as a ‘sand hammer’, while standing in the pool and wearing a swim mask, to reduce the edges of sand divots (or gopher tunnels!).

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