How to Find and Fix a Pool Leak (The Bucket Test)

In this guide: Leak or evaporation? · The bucket test · Finding the leak · Fixing it · Calculators

Every pool loses some water to evaporation — a warm, windy, uncovered pool can drop a quarter-inch or more a day and be perfectly sound. The question is always: is this normal evaporation, or a genuine leak? One simple test settles it before you spend a dollar.

Leak or just evaporation?

Evaporation and a leak both lower the water line, so you can't judge by drop alone. Evaporation is driven by heat, wind, humidity, and sun; a leak loses water regardless. The trick is to compare your pool against a control that can only evaporate — a bucket.

The bucket test — the standard method

1. Fill a bucket with pool water and set it on a pool step so it's partly submerged (matching water temperatures).
2. Mark the water level inside the bucket and the pool level on the outside, at the same moment.
3. Wait 24 hours with the pump running normally (run a second 24-hour test with the pump off to isolate plumbing leaks).
4. Compare. If the pool dropped the same as the bucket, it's evaporation. If the pool dropped more, the difference is your leak.

The evaporation/leak calculator turns that difference into gallons per day so you know how serious it is — and whether it's worse with the pump on (pressure-side plumbing) or off (structure or suction side).

Narrowing down where it leaks

Watch where the water stops dropping — that level often reveals the leak's height (at a skimmer throat, a return fitting, or a light niche). Leaks that worsen with the pump running point to pressure-side plumbing; leaks only when it's off suggest the structure or suction line. A few drops of dye near suspected spots (with the pump off) will get pulled toward a crack.

Fixing it

Fitting and skimmer leaks are often a pool putty or sealant repair. Vinyl-liner punctures take a patch kit (many work underwater). Cracks in plaster or a suspected underground plumbing leak usually warrant a professional with pressure-testing gear — chasing a buried pipe by digging is rarely worth it. Fixing leaks isn't just cost: the EPA's WaterSense program highlights pool leaks as a meaningful source of household water waste.

Do the math on this page

These calculators turn the steps above into your exact numbers:

Evaporation / leak testBucket-test comparison Pool cover savingsWater & heat payback Water fill costGallons × your local rate

Sources & standards

This guide is built on published health codes, national standards, and government energy guidance. For the exact equations behind the linked calculators, see our formula reference.

U.S. EPA WaterSense — Fix a Leak Week — the EPA WaterSense leak-finding campaign and why fixing leaks saves water
U.S. EPA WaterSense — Pool Water Efficiency — EPA guidance on pool water efficiency and loss
U.S. Department of Energy — Energy Saver: Swimming Pool Covers — how covers cut evaporation, the loss the bucket test controls for
Pool & Hot Tub Alliance (PHTA) — ANSI-accredited standards — industry standards for pool construction and fittings

This guide is general information, not a substitute for your local health code or a licensed professional. Always follow the dosing instructions on your chemical labels and confirm readings with a test kit.