Swimming Pool Blog

Leaking Pool ~ How to find a pool leak

by Sean Griffin, May 31, 2009

It's not uncommon for pool owners to notice that water seems to be leaking out of their pool after opening it for the year. But where is the leak coming from? Let's take a look and see how to find and repair swimming pool leaks.

First of all, you have to make sure that it really is a leak in the first place. What do you think is a leak, may be something else. There are actually three main causes of water loss from swimming pools and they are:
1. Swimming pool plumbing leaks

2. Swimming pool shell leaks

3. Normal evaporation or excessive splash
So before you go any further let's rule out number three in the list above. It's important to do this, because actually the sun can evaporate quite a bit of water from a pool on a daily basis without your realizing it, and swimmers can splash a lot of water out of a pool too. On a hot day, a pool can evaporate up to 1/4" per day! More on a windy day. Cover your pool with an automatic pool cover or a solar blanket or liquid solar blanket. Solid fences or hedges to serve as wind breaks can help. A shaded pool will evaporate less than a fully sun exposed pool as well.
To find out for sure if the water loss is due to evaporation or not, take a fairly large container and fill it with water and place it on the first step of your pool. Then remove enough water from the container so that the water level in the pool and in the container is exactly the same. Now leave the container there for a couple of days to see what happens with no one using the pool in the meantime. If after a couple of days the water level in the pool has gone down, and the water level in the container has gone down the same amount, then you know that the water loss you are experiencing is most likely just evaporation due to the sun. On the other hand, if the water in the pool has gone down farther than the water in the container, then most likely there is indeed a leak in your pool somewhere.
To find a pool leak, the first place to inspect is around your filter and pump. Do you notice any water spots or damp areas there? If so, try to trace back where the water is coming from. Very often, it will be a connection on one of the pipes in this particular area.You may need to turn on the pump for a while and observe it to see if any leaks develop while everything is running. If the leak begins to show, and you feel comfortable with repairing the pool plumbing, then this is a job that you may wish to do yourself. However, for most people it will be a job that is best left to a pool professional.

In order to determine whether or not the leak in the pool is in the plumbing or in the shell of the pool, you would isolate the plumbing. This means to plug all the holes in the pool. Plug the skimmer and the return fittings, cleaner fittings, vacuum lines, main drain (if possible) with expandable freeze plugs or threaded plugs.

If no obvious leaks can be found in the plumbing, then perhaps the leak is in the shell of the pool itself. If your pool is gunite, your plaster is a water proof shell over top of concrete. Much tougher than vinyl. The most common area in a gunite pool will be the interface of the plastic skimmer with the concrete pool. If you lay down on the deck, over the skimmer lid, and look upside down into the skimmer throat, you will see the white plastic square rim of the skimmer. On the bottom and sides, if you notice cracks, you may have a leak there, especially if you notice small leaf debris stuck in (sucked in) to the cracks. To double check, shut off the pump, and perform a dye test, watching for any dye getting sucked into the crack. The professional will use a dye syringe, but you can also use food coloring or your pH reagent (be sure not to suck in any water or you'll dilute and ruin your reagent).
Other areas besides the skimmer to locate leaks in a gunite pool include:
  • Bare spots on the plaster. Use a plaster mix to repair. Pool Plaster is waterproof, gunite is not.
  • Underwater light fixtures. What leaks is not the fixture itself, but the conduit running from the light niche to the junction box. Use a cord stopper to repair.
  • Leaks at wall return fittings. With pump turned off, again dye test for leaks.

If you have a vinyl lined pool, small holes can leak a lot of water. They are usually not too hard to find however. To locate a leak in a vinyl liner pool:

  • Turn off pump and dye test around skimmer plate, and all wall fittings, underwater lights and drop in step, seat or spa sections.
  • Inspect closely the corners of the pool, especially where the liner fits tightly. Look for dark spots or leaf debris stuck to the liner.
  • Inspect any ladders to make sure ladder bumpers are in place and the ladder has not cut a hole through the pool liner.
  • Look for areas of the sand which appear to have washed away or eroded.
  • Look for slight staining on the walls, which may indicate rust through.

When you find the leak in a vinyl liner, make a good repair. If you can lower the water to the point of repair you will get a better bond. Use a patch that is rounded, and is several times larger than the hole itself. Clean and dry the area if possible and apply light pressure for 1 minute after patching, then keep fussing with the edges to keep them from curling up. Use Flexible Sealer to repair. Or you can use a vinyl patch kit. The clear patch material is easy to work with, but these tend to yellow over time, so a matching piece of your own vinyl is better, if you are fortunate enough to have kept the pieces they cut out for the skimmer and the returns, or have a sample piece.

Finally, we turn to pool leaks that are actually not leaks at all, but splash out and backwash water.

Backwashing....can't avoid it. Just don't overdo it so that you have to add water again. Some communities are now outlawing backwashing, instead requiring cartridge filters to be installed on all new pools. Of course water is used to clean cartridges as well, but maybe not as much as backwashing a sand or DE filter.

Splashout! No more cannonballs! OK, have fun, enjoy the summer and remember to be safe, and all you pool guys "Shut the Gate!"

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