Pool Bucket Test: Leak or Evaporation? Calculator

Evaporation takes the same amount from the bucket and the pool, because both sit in the same sun, wind, and heat. So the bucket shows you what evaporation alone would do this week, and the calculator turns the difference into gallons and dollars.

How to do the bucket test

These steps follow the bucket test published by the City of Chandler, Arizona.

Turn off the automatic fill valve, if your pool has one, and don't add water during the test.
Set a bucket on a pool step so its rim stays above the water. Put a brick or a large rock in it so it doesn't move.
Fill the bucket with pool water to the same level as the pool.
Mark the water level inside the bucket with tape or a water-soluble marker.
Mark the pool level on the outside of the bucket.
Wait at least 2 to 3 days. Don't swim, backwash, or splash water out. If it rains, start over.
Measure how far each level dropped, to the nearest 1/8 inch, and enter both numbers in the calculator.

A longer test is more accurate: on day one both drops are small, and a 1/8-inch reading error is a big share of the answer.

How the calculator turns two drops into gallons a day

Enter your pool's water surface (or its length and width or diameter), the pool drop, the bucket drop, and the number of days. The example is a 32 × 16 ft pool with 512 sq ft of water surface. At that size, 1 inch of water is 319 gallons (1,208 L).

Bucket drop: 0.25 inch a day, or about 80 gallons a day. That is your evaporation this week.
Extra pool drop: another 0.25 inch a day, or about 80 gallons a day. That water is not evaporating.
Over 30 days: the extra loss adds up to 2,394 gallons, about $19 of water at an example price of $8 per 1,000 gallons.

The formula: gallons = water surface in square feet × inches of drop × 0.623. One inch over one square foot is 0.623 gallons. Use the water price from your bill. If you don't know your pool's surface or size, the pool volume calculator works it out.

How much evaporation is normal

There is no single normal number. Evaporation depends on water temperature, air temperature, humidity, wind, and sun, so it changes week to week. That is exactly why the bucket test works: it measures your own evaporation in your own weather.

Orenda Technologies, a pool chemical company, gives 0.25 to 0.5 inch a day for an outdoor pool in summer. Treat this as a rough guide from one company, not a standard.
The City of Chandler says an average pool there can evaporate 20,000 gallons in a year. That is a hot desert climate. A humid or cooler climate loses less.
The U.S. Department of Energy (DOE) notes that warmer water, stronger wind, and lower humidity all raise the evaporation rate, so heated pools lose more. A loss that seems high in a cool week is worth a test.

If the level drops in cool, calm, humid weather, or the pool needs water much more often than last summer, test before you assume it is the heat. For how high the water should sit and how to top it up, see pool water level. For summer care, see pool care in hot weather.

What your result means

Pool and bucket dropped the same. It is evaporation. A pool cover is the main way to cut it.
Pool dropped more than the bucket. Water is leaving another way. If the difference is bigger than you can read on the marks (the calculator uses 1/8 inch as an example), repeat the test once to confirm.
Bucket dropped more than the pool. Something is off with the test: the bucket may be leaking or sitting in direct sun while the pool is shaded, or rain or a fill valve may have added water to the pool. Repeat the test.

The test tells you whether there is a loss, not where it is. It also can't catch a slow leak that is smaller than your reading error.

Next step: pump on vs pump off

Many pool technicians run the test twice: once with the pump running on its normal schedule and once with the pump off for the whole test. If the pool loses more with the pump running, the leak is more likely on the pressure side of the plumbing or equipment (from the pump to the return jets). If it loses the same either way, the shell, liner, fittings, or lights are more likely. We did not find a manufacturer or government source for this step, so treat it as a common practice, not a rule.

Simple checks you can do yourself while you wait:

Look for wet soil, soft spots, or puddles near the equipment pad and along the plumbing path.
Check the pump, filter, and valves for drips while the pump runs.
On vinyl and above-ground pools, look for wet spots under the wall and around the skimmer and return fittings.
Watch where the level stops dropping. If it stops at the skimmer, a light, or a return, the leak is often at that height.

What a leak costs in water and chemicals

The water itself is usually the smaller cost. Leaking water takes its chemicals with it, so a leaking pool needs more chlorine and more stabilizer (cyanuric acid, CYA) to stay where it was. Fresh top-up water also brings its own calcium and alkalinity. If you top up the pool every few days, the frequent filling can also hide a slow leak.

Evaporation is different: it takes only water and leaves calcium, salt, and CYA behind, so those slowly build up over a season. If yours have climbed, see how often to drain a pool. To price the top-up water, the pool fill cost calculator uses the same water price.

When to call a leak-detection pro

The test shows extra loss twice in a row.
You see wet ground, cracks, or the deck moving.
The leak is in buried pipes, the main drain, or a light niche.
Your pool is inground and you would need to lower the water a lot to reach the leak.

Leak-detection companies often use pressure tests, dye, and listening equipment to find the spot. Bring your bucket test numbers: they show how big the leak is.

FAQ

How long should a pool bucket test take?

At least 2 to 3 days, the time the City of Chandler suggests. A longer test is more accurate, because a small reading error matters less when both drops are bigger. Start over if it rains or if anyone adds water.

Is my pool leaking or evaporating?

Compare the pool drop with the bucket drop over the same days. If they match, it is evaporation. If the pool drops more, the difference is a leak. In our example, the pool lost 0.75 inch more than the bucket in 3 days, about 80 gallons a day beyond evaporation.

Why is my pool losing water if there is no leak?

Evaporation, splash-out, and backwashing all lower the level. Evaporation is highest in hot, dry, windy, sunny weather, and in heated pools. Orenda gives 0.25 to 0.5 inch a day for an outdoor pool in summer. If the bucket test shows the pool and bucket dropping the same, the loss is evaporation.

Can I run the pump during a bucket test?

Yes. Run it on its normal schedule for the first test. If the pool loses more than the bucket, a second test with the pump off for the whole period helps show whether the loss is in the plumbing or in the pool itself.

Sources

City of Chandler, Arizona, Pool care (bucket test steps; 20,000 gallons a year): chandleraz.gov
U.S. DOE Energy Saver, Swimming pool covers (what raises evaporation; archived copy, May 2026): energy.gov via web.archive.org
Orenda Technologies, Evaporation and accumulation (0.25–0.5 in per day in summer; secondary source): blog.orendatech.com
Unit conversion: 1 cubic foot = 7.48 US gallons, so 1 inch over 1 sq ft = 0.623 gallons (same constant our volume calculators use): methodology