How do I find a leak in my pool?

A pool that keeps dropping is either evaporating or leaking, and a bucket test tells you which. Set a bucket of water on a pool step, mark the water level inside the bucket and outside it, and compare the two a day later. Evaporation lowers both equally; a leak lowers the pool more.

Know what a normal loss looks like

Some loss is normal. The EPA's pool water efficiency guide says that if your pool is losing more than 2 inches of water per week, or 3 inches in hot, dry areas with high evaporation rates, then it is likely you have a leak.^[1] Wet spots around the pool, or air bubbles in the water return pipeline or in the pump strainer, can also be signs of leakage.^[1]

To know your weekly loss, add water by hand for a while rather than letting an automatic fill do it quietly. The EPA suggests exactly that, so you are aware of your pool's weekly water loss.^[1]

Run the bucket test

The EPA calls this the do-it-yourself leak test, and the City of Tampa's water department describes it the same way.

1. Pick a day without rain or heavy winds. Shut down all pool systems (filtration systems, pool cleaners, automatic fills, etc.) and close the pool for 24 hours.^[1]
2. Fill a 2.5- to 5-gallon bucket to about 1 inch from the top and set the bucket in the pool (on a bench or step) so that at least two-thirds of the bucket is submerged in the pool, with the bucket water level a little higher than the pool level.^[1]
3. Mark the initial water level inside the bucket with a marker or a piece of tape, then mark or measure the still pool water outside it the same way.^[1]
4. Leave it for 24 hours, then record both levels again. If pool water loss is greater than bucket water loss, the pool may have a leak.^[1]

Tampa lets the test run longer, 24 to 72 hours, with the same instruction to compare the two losses.^[2] A longer test shows a slow leak more clearly. If the two levels fall by the same amount, the water is evaporating, not escaping, and you can stop worrying.

Narrow down where it is going

If the bucket says you have a leak, look for the clues before you call anyone.

Repeat the test with the pump running. If the pool loses noticeably more water while the pump runs, the leak is often in the pressurized plumbing, the pump or the filter. If it loses about the same either way, the shell, liner, skimmer or a fitting in the wall is more likely. This is a rule of thumb, not a diagnosis.

Walk the equipment pad. Look for wet ground, drips at the pump seal and strainer lid, and wet fittings around the filter. The EPA lists the places leaks turn up: the pool liner, the pump seal, pool piping, the pool-to-pipe connection, pool edges, and pipe joints.^[1] Keep your hands away from any wiring that is wet.

Watch the water return and the strainer. Air bubbles in the return line or the pump strainer can be a sign of a leak.^[1]

Check the automatic fill. Fill valves can sometimes malfunction and send water to a pool's overflow drain. To confirm yours shuts off properly, plug the overflow drain and monitor whether the pool level is rising; if it is, the valve may be stuck open and should be repaired or replaced.^[1] If your pool has an automatic refill, the EPA says to shut it off for 24 hours once every three months to test for leaks.^[1]

Look at the surroundings. Soggy patches in the lawn, a sunken area of decking or a crack in the coping all point toward the water's path. Take photos and note the date; a contractor will ask.

What a leak costs you while you wait

Water adds up quickly. Tampa's water department says it takes about 600 gallons to fill up an average pool by 2 inches.^[2] The EPA warns that small leaks can quickly turn into big leaks if they go unattended.^[1] Do not leave a confirmed loss for the rest of the summer.

Stop and call a pro if

• The bucket test shows a leak and you cannot find it. A pool leak-detection specialist or a licensed pool contractor can pressure-test lines and inspect the shell.
• The water loss is large, or the level drops overnight.
• You see cracks, a bulging wall or a sunken deck. That is a structural problem, not a plumbing one.
• Water is near the pump motor, the light or other wiring. Stay clear and call a licensed electrician.
• Air bubbles keep showing up in the return line or pump strainer. The EPA lists them as a sign of leakage, and a pro can trace where the air is getting in.^[1]

Getting help in Virginia

If the test shows a leak, read who to call to fix a leaking pool and what pool leak repair costs in Virginia. For the routine side of keeping a pool in shape, see how to clean a swimming pool, browse all pool and spa answers or look at local pool pros.

When you are ready, describe the leak and licensed local pros can quote it.