Pool Leak vs Evaporation Bucket-Test Calculator

The bucket test pits your pool against a control. The bucket loses water only to evaporation; the pool loses water to evaporation and any leak. Subtracting the bucket's drop from the pool's drop isolates the leak: net loss = pool drop − bucket drop. Because the bucket sits in the same sun and wind as the pool, it's a far more reliable signal than any fixed "quarter-inch a day" rule of thumb, which is a Southern-California-climate guideline, not a hard line.

netDropIn        = poolDrop − bucketDrop          (the netting)
netDropInPerDay  = netDropIn × (24 / testHours)   (normalize any test window)

rectangular: galPerDay = length × width      × netDropInPerDay × 0.6233
round/spa:   galPerDay = diameter × diameter × netDropInPerDay × 0.48929

galPerHour   = galPerDay / 24
galPerMinute = galPerDay / 1440
cost/day     = (galPerDay / 1000) × your rate   (× 30.4 month, × 365 year)

We always apply the gallons formula to the net loss, never the raw pool drop — using the raw drop would count evaporation as a leak and overstate the loss. We also normalize to a per-day figure before judging the verdict, so a 48-hour test is correctly halved rather than read as twice the leak. The constants (0.6233 gallons per ft² per inch, rectangular; 0.48929 on diameter² for round pools and spas) assume feet and inches, so any centimeter or meter input is converted first.

Reading the verdict. The net per-day difference bands as: equal drops → no leak (normal evaporation); up to a quarter-inch → borderline (re-test to confirm); a quarter to a half-inch → possible leak; more than a half-inch → likely leak. A possible or likely result is a prompt to book a professional leak inspection, not a diagnosis — this tool doesn't assert a leak exists or locate one.

Sources: American Leak Detection — Calculate Your Swimming Pool Water Loss in Gallons; Pool Leak Inspections — Bucket Test; PoolDial — Bucket Test Calculator.