How to tell if a pool on your route is leaking or just evaporating

Set up the bucket test with the right controls

The bucket loses water to evaporation only. The pool loses evaporation plus any leak. The gap between the two is the leak. The test costs five minutes on a stop and a second look on the next visit, and it hands the customer a number instead of an argument.

Skip any of these steps and the result won't hold up.

• Fill a clean 5-gallon bucket with pool water and set it on the second step, so it sits partly under and stays at pool temperature. A bucket on the deck bakes in the sun and evaporates faster than the pool, which fakes a leak.
• Mark the water level inside the bucket and the pool level outside it, on the same wall, with tape or a grease pencil. Two marks on one surface make the next reading obvious.
• Leave the pump on its normal schedule and change nothing else, so the pool runs under the conditions it lives in every week.
• Shut off the autofill and tell the customer not to swim, backwash, or drain until you read it. An autofill topping off mid-test is the biggest reason a test comes back inconclusive.
• Read it at 24 hours and confirm at 48. Rain voids the test, so start over. A gap under about an eighth of an inch is test error and proves nothing. A half inch or more over 48 hours is a leak.
• Compare the gap between the two marks, not the total drop. Both levels falling together is evaporation, however big the total looks. The pool dropping below the bucket is a leak, and the gap is about the size of the leak.

Know the evaporation number before you test

Typical summer evaporation is about a quarter inch a day, or 1.5 to 2 inches a week. Hot, dry, full-sun weeks in July and August run 2 to 2.5 inches. Wind adds about 0.5 to 1 inch. A heated pool, a spa or a running waterfall adds 1 to 2 inches, and a waterfall alone can double the loss. A cover cuts a week's loss to about 0.5 to 1 inch. Treat these as typical ranges. Your route will settle into its own numbers within a season.

Turn the loss into gallons. An inch off a 400-square-foot pool is about 250 gallons. A pool running 2 inches a week over baseline loses about 500 gallons a week, and that's the number to give a customer who pictures a slow drip.

• Compare the pool to other pools on your route on the same day. Two pools four streets apart in the same heat are the cleanest control you'll get.
• A pool that started needing the hose after a water feature went in, or after the cover came off, has already explained itself.
• Rule out your own work before you call it a leak. A backwash moves a few hundred gallons and a vacuum to waste can move over a thousand. Note either one in the record, the same way you'd note clearing sand out of a pool after a filter failure.

Stabilizer and hardness flag a leak first

Evaporation takes out pure water and leaves every dissolved mineral behind. Calcium hardness and salt climb while cyanuric acid (stabilizer) holds steady. A leak carries water out, and the fresh fill has no stabilizer in it. So cyanuric acid drifts down while hardness moves toward whatever your fill water runs.

Rising hardness is the expected half. The post on why calcium hardness climbs in refilled pools covers the same mechanism from the other end. The tell is the pairing. Hardness up with stabilizer sliding means the pool is taking on far more fill than the weather explains. Hardness up with stabilizer steady is a hot month.

A pool in Peoria, Arizona needs the hose every visit for three weeks. August evaporation there runs about a quarter inch a day, so 1.75 inches a week is normal. This pool is down closer to 4. Its log shows calcium hardness rising from 310 to 425 ppm over six weeks on hard fill water, while cyanuric acid slid from 60 to 41 ppm instead of holding. That pattern is dilution, not evaporation. A 24-hour bucket test confirmed it, and the customer got a documented finding.

None of this works from one visit. You need the same readings, taken the same way, for a couple of months. Any system where you can log readings at every visit and see the history per pool will show the pattern. PoolBoss keeps the readings on the pool record, so you can read a pool's history across visits without paging through one visit at a time.

Treat it as a signal, not proof. Cyanuric acid breaks down on its own over a season, so a slow drift means little by itself. Look for a slide faster than the rest of the route shows. Heavy rain, a big splash-out week or a partial drain dilutes stabilizer the same way a leak does. The chemistry tells you where to point the bucket, and the bucket settles it.

A strip pad reads cyanuric acid within about 30 ppm, which is wider than the drift you're hunting. Use a liquid test kit for this, and read up on which readings a strip can and cannot be trusted for before you build a diagnosis on a trend.

An autofill can hide a leak for months

A working autofill holds the level at the tile line every week while a leak runs underneath. The tech sees no symptom for a season. The first sign is the customer's water bill, or a reading that stops making sense.

A quarter inch a day lost on a 400-square-foot pool is about 62 gallons a day, or near 1,900 gallons a month, on top of the evaporation the autofill already covered. On a metered supply that shows up as a jump in the bill.

With the level pinned, watch three signals. Stabilizer sliding while hardness climbs, on a pool nobody drained, is the strongest. The water bill is the bluntest, so ask the customer for it. The third is the fill valve. If it runs more than the valves on neighboring pools, or the customer hears it at night, that's the signal the level would have given you.

To test a pool on an autofill, shut the fill off for the 24 to 48 hours and tell the customer it's off so nobody turns it back on. Switch it on again after you read the result. A test with the autofill live measures nothing.

Give the customer numbers, then hand off the repair

Report what you measured, not a diagnosis. You can say the pool is losing more water than evaporation explains, how much, and over what period. Whether the cause is a cracked skimmer throat, a failed light conduit or a break under the deck belongs to a licensed leak detection company. Guessing in the driveway turns a service call into a liability.

A good finding names the expected loss for the conditions, what the pool lost, the bucket result and the chemistry trend. For example, the pool is losing about 4 inches a week where its neighbors lose 1.75, the bucket showed the pool half an inch below it after 24 hours, and stabilizer fell from 60 to 41 ppm since June. A leak company can start from that.

Put it in the visit notes with photos of the water line and the marked bucket, so it lives on the pool and not in a text thread. It's the same habit as keeping the readings worth logging at every stop. If you do the repair work, quote it off that visit. If you don't, the notes are what the specialist reads.

Tell the customer what you'll keep doing in the meantime. A pool topped off all the time keeps pulling stabilizer down and hardness up, so expect to correct the chemistry again after the repair. Charge for diagnostic time as a named line item. Customers accept paying for an answer far more readily than a surprise.