Pool Leak vs Evaporation: How Can You Tell?

Put a bucket of water in the pool and compare the two drops over the same 24 hours. That's EPA's bucket test. If the pool drops more than the bucket, you may have a leak and a leak professional should look for it. The test won't tell you where the leak is, only that you're losing more than evaporation explains.

Why doesn't one "normal" daily drop fit every pool?

EPA's Pool Water Efficiency page lists four ways pools lose water: evaporation, pool cleaning, leaks and splashing.

EPA's guide, Jump Into Pool Water Efficiency, says evaporation depends on temperature, humidity and wind speed, so hot, dry, windy days pull more water out. The guide was written for home pools, but EPA says many of its tips also apply to commercial pools.

What are the warning signs of a leak?

EPA lists these signs:

• Water loss that a bucket test says is more than evaporation.
• Wet spots on the ground around the pool.
• Air bubbles in the water return line or the pump strainer.

EPA also says leaks are often found in the liner, the pump seal, the pipes, where the pool meets a pipe, the pool edges and pipe joints. It suggests a water meter on the fill line so you can see how much water you add. If the pool has an automatic fill, EPA suggests shutting it off for 24 hours every three months to check for leaks.

EPA's home pool guide says losing more than 2 inches a week (or 3 inches in hot, dry places) likely means a leak. Treat that as a home-pool rule of thumb, not a limit for your commercial pool.

What should you record before testing for a leak?

Make a simple water loss record. Use the same measuring point each time and say how you measured. A photo helps the next person find the spot.

Include:

• Pool name, date, and start and finish times.
• Water level at start and finish, with the unit.
• Rain, wind and temperature.
• Whether swimmers used the pool.
• Water added or drained, with time and amount if known.
• Cleaning, backwashing, service work or equipment changes.
• Who took the readings.

Mark unknown amounts as unknown. Don't turn "the hose ran for a while" into a number.

Between tests, keep one weekly "water added" row per pool as a measured check on Poolean's leak flag. Over a few weeks it shows whether the pool needs extra water:

Date	Meter reading	Gallons added	Auto-fill on/off	Weather	Notes
Start of the week	Number on the fill-line meter	This week's meter number minus last week's	Was the automatic fill on?	Hot, dry, windy or rainy	Backwash, cleaning or repairs

Keep these notes with your commercial pool maintenance schedule so earlier work on the same equipment is easy to find.

How does a pool bucket test work?

EPA's guide gives these steps:

1. Pick a day with no rain or heavy wind.
2. Shut down pool systems (filter, pool cleaners, automatic fill) and close the pool for 24 hours.
3. Fill a 2.5- to 5-gallon bucket to about 1 inch from the top.
4. Set it on a step or bench so at least two-thirds of it is under the pool water.
5. Mark the water level inside the bucket and the pool level, using tape, a marker or a ruler.
6. After 24 hours, measure both again.

If the pool lost more water than the bucket, the pool may have a leak.

At a commercial pool, shutting off the filter and closing for a day is a big step, and your health department may have rules about it. Have the trained operator plan the test, and never stop water treatment while swimmers are in the pool.

How do you compare the measurements?

Made-up numbers, not a normal limit: say the pool level drops 8 millimeters (mm) over 24 hours and the bucket drops 3 mm. The difference is 8 − 3 = 5 mm.

The pool lost 5 mm more than evaporation explains. That's a reason to call a leak professional. It doesn't prove a pipe is broken or tell you how much the leak releases.

Use your own numbers the same way: pool drop minus bucket drop, same unit, same time period. If it rained or someone added water, write it down and ask the professional whether the test needs to be repeated.

Who should you call, and what should you send?

Use this simple rule:

Result	Next step
Pool and bucket dropped about the same	This test shows no extra loss. Keep logging water added each week.
Pool dropped more than the bucket	Call a leak detection professional. Send the readings and notes.
Wet spots, bubbles in the return line or strainer, or water near equipment	Tell your manager and the trained operator now, and book a professional.
Water near electrical equipment or anyone hurt	Follow the emergency plan and call emergency services.

Ask the professional for a written finding, the repair needed and the next check. Do not mark the issue fixed just because a visit is booked. Follow equipment instructions, chemical labels and your health department during any repair.

Poolean's water model uses each pool's size, sun, temperature and swimmer count to estimate daily water loss. It flags a possible leak when the loss is higher than the weather explains. Treat that flag as a reason to check, then track the repair in Poolean's maintenance tools. You can book a 30-minute call to see it. For a morning review across sites, see our guide to managing multiple pool sites.

The short version

• EPA's bucket test compares a pool's drop with a bucket's drop over 24 hours.
• A bigger pool drop may mean a leak; it does not show where.
• Watch for wet spots and air bubbles in the return line or pump strainer.
• Record levels, weather, water added and recent work together.
• Let a trained professional plan the test and find the leak.