My Pool Water Level Dropped After Closing: Leak or Normal?

Hey everyone, Al here! In my last post, I walked through how to winterize your pool the right way. Once the cover goes on, though, a new question usually pops up: “Al, why is my water level dropping?” A small change can be normal, but a steady drop deserves attention before cold weather turns a simple fix into spring damage.

First, Mark the Water Level

Start with the simplest test: mark the waterline with a piece of painter’s tape or take a clear photo against a step, tile line, or skimmer screw. I like the photo method because there is no guessing later. Check it again after 24 to 48 hours. A one-time change after closing may come from water displaced by the cover, water removed during final plumbing work, or a little evaporation before the cover was secured.

A level that continues to fall at roughly the same pace every day should be treated as a likely leak. Repeatedly topping off the pool only hides the pattern.

Where the Water Stops Is a Clue

• At the skimmer: Inspect the skimmer faceplate, gasket, throat, and winter plug.
• At a return fitting: Check the plug, fitting, and surrounding liner.
• Below every wall fitting: Look closely for a liner tear or a possible underground-line problem.
• Only when the pump runs: During the season, that often points toward pressure-side plumbing or equipment.

For a closed pool, a loose or poorly sealed winter plug is one of the first things our technicians check. Our winter supplies collection includes several plug styles, but the diameter and fitting type have to match your plumbing.

Do Not Drain the Pool Too Far

Never drain an in-ground vinyl pool just to chase a leak. The water supports the liner, and removing too much can cause shifting, wrinkles, or floating when groundwater is high. Keep an eye on the cover as well. A solid cover collecting rainwater can press down and make the pool level look different from the deck.

If the loss is fast, continues below the fittings, or the source is not obvious, the pool needs a proper leak-detection check before freezing weather arrives. Catching it now is much cheaper than discovering a damaged liner or plumbing line at opening.

The Bottom Line

Mark it, measure it, and watch where it stops. I’ve found that a little patience usually shows whether the change is normal settling or a real leak. In the next post, we’ll stay up at the surface and compare solid winter covers with mesh safety covers—because the type of cover you own changes what you should expect all winter.