Sprinklers are minutes × how much the zone actually puts down. A single zone can throw many gallons per minute. Several zones on a timer every other morning is one of the largest water lines a house can have — larger than indoor fixtures for a lot of suburban lots.
Rain does not always cancel a dumb timer. A broken head that fogs the sidewalk is a leak wearing a zone number. Early morning usually wastes less to wind and sun than noon, but it does not change the gallons the nozzle emitted.
Drip irrigation is a different, usually lower, card. This page is spray/rotor lawn zones.
Set a typical zone flow and minutes per watering, times days per week. A stuck valve is Leak / drip.
At 5.00 per 1,000 gallons, 12 gallons per minute for 15 minutes is 180 gallons — about 0.90 per zone run. Four zones, three days a week, is a monthly volume you can see without walking the lawn.
Zones
Four zones three mornings a week is not one 15-minute run. A stuck valve is Leak / drip. Drip irrigation is a lower-flow card if that is what you have.
Related
Usage estimate only — not a utility bill, load calc, or advice.