Arizona-specific technical guide
Arizona Pool Losing Water? The Truth About Evaporation vs. a Real Leak
A deeper Arizona-specific explanation of ETo, AZMet weather context, seasonal patterns, bucket testing, and measured pool water loss.
Published 2026-06-25 | Updated 2026-08-30 | 5 min read | By Echo Leak Detection
Why Arizona advice needs nuance
Generic national pool advice often undersells desert evaporation. Heat, low humidity, wind, and intense solar exposure can all increase water loss, so Arizona homeowners need measured comparisons instead of a single universal number.
What ETo can and cannot tell you
Reference evapotranspiration, or ETo, is a weather-station estimate of evaporative demand. It is useful context, but it is not literally the same thing as open-water pool evaporation. A bucket test gives a more direct pool-side comparison.
AZMet weather context
The University of Arizona AZMet network publishes daily data through a JSON API, including ETo fields such as eto_azmet_in and eto_pen_mon_in. Echo uses this as context in the evaporation checker while clearly separating weather context from proof of a leak.
Why the nearest station is not your backyard
A weather station may be miles from the pool and cannot see its shade, walls, wind exposure, water temperature, cover, spillways, or swimmer activity. Station data is useful for understanding regional evaporative demand, but the bucket sitting beside the pool experiences conditions much closer to the water you are measuring.
Season and equipment change the pattern
Summer heat can produce obvious evaporation, while wind can accelerate loss during any season. Heated spas, vanishing edges, fountains, spillways, aeration, and long pump schedules increase exposed or moving water. A cover can reduce evaporation. Compare measurements under similar operating conditions instead of treating one day as a universal baseline.
Patterns that change the diagnosis
Water loss that greatly exceeds a bucket test, appears during cooler months, changes with pump operation, or leaves wet soil around the pool is more suspicious than water loss that tracks with weather conditions.
Use gallons to understand the scale
One inch of water across a large pool represents hundreds of gallons. The evaporation checker converts the unexplained inch difference into an approximate daily gallon amount using the entered surface area. That estimate helps communicate scale, but an accurate pool shape and repeated measurements produce a better planning number.
Why diagnose before repair
Guessing can send money toward replastering, equipment replacement, or excavation that does not address the source. A measured diagnosis narrows the repair decision before work begins.
When to call for leak detection
Call when repeated bucket tests show additional pool loss, the autofill masks a persistent drop, wet areas develop, equipment draws air, or water loss changes by operating mode. Turn off the autofill long enough to measure only when it is safe for the equipment and pool finish, and never let the water fall below the level needed for proper circulation.
Not sure what your water loss means?
Use the evaporation checker, then call Echo if the measurements point toward unexplained water loss.