Measure first, then schedule
EPA WaterSense recommends placing several identical containers around a lawn and timing how long the sprinklers take to apply about half an inch. The actual readings help reveal uneven coverage that a nominal sprinkler specification cannot show.
Precipitation rate = average catch depth ÷ test minutes × 60
Gallons applied = area in sq ft × target inches × 0.623376
Low-quarter distribution uniformity compares the average of the lowest quarter of readings with the average of all readings. It is a coverage diagnostic, not the same thing as overall efficiency.
Reduce runoff without reducing required minutes
When water begins to pool, the same total runtime can be split into shorter cycles separated by soak periods. EPA notes that clay-rich soils and slopes may benefit when irrigation is applied in intervals rather than one continuous run.
The tool uses the runoff time you observed. It does not infer a precise infiltration rate from a generic soil label.
Use cost and repair evidence together
Compare expected and measured zone flow, record visible problems, and repeat the measurement after repairs. EPA recommends monthly inspection for leaks, broken or clogged heads, and water spraying onto pavement.
The cost estimate includes only the variable rate you enter. Fixed service charges, minimum bills, drought surcharges, and tiered pricing may require a separate utility calculation.
Controller savings are a scenario, not a promise
EPA says WaterSense-labeled weather-based and soil-moisture-based controllers can reduce unnecessary irrigation. Its national reference says an average home may save up to 15,000 gallons annually when replacing a clock-based controller, but a specific property can save more or less.
Use your own baseline, expected savings percentage, rebate, installation cost, and local rate rather than treating the national reference as a guaranteed result.
Sources and boundaries
This calculator does not replace a certified irrigation audit, local watering rules, backflow requirements, hydraulic design, electrical work, or plant-specific advice.
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