Short answer
A high water bill in the Phoenix area usually comes from one of four things: a running toilet, an irrigation leak, a slab leak, or seasonal watering. Turn off every fixture and the irrigation controller, then watch the meter's leak indicator. If it moves, you have a leak, and a few simple shutoff tests tell you where.
First, compare the right months
Valley water use swings hard with the seasons because irrigation and pools use far more in summer. Compare this month's bill to the same month last year, not to last month. A 30% or larger jump over last year with no change in habits is worth investigating.
Do the meter test
Your meter is usually in a box near the street or sidewalk. Lift the lid carefully, since scorpions and spiders like meter boxes.
- Turn off every faucet, the dishwasher, washer, ice maker and irrigation controller.
- Find the small leak indicator on the meter face (often a red triangle or star).
- Watch it for two minutes. If it turns, water is going somewhere.
Narrow it down
Now split the house from the yard.
- Close the house shutoff valve. If the meter stops, the leak is inside the house. If it keeps turning, it's between the meter and the house, or in the irrigation mainline.
- Inside, put a few drops of food coloring in each toilet tank. Color in the bowl after 15 minutes means a leaking flapper.
- Close the cold inlet on the water heater. If the meter slows or stops, suspect a hot-side slab leak.
The usual suspects in Valley homes
Toilet flappers and fill valves wear out faster in hard water. Irrigation mainlines leak quietly under desert landscaping. Slab leaks on copper hot lines are common in homes built from the 1960s through the 1990s.
When to call a plumber
- The meter moves with everything off and it isn't a toilet.
- You find a warm spot on the floor or hear running water.
- The yard has a soggy or unusually green patch between the meter and the house.
What the plumber does: see slab leak detection.
Common questions
Can a running toilet really raise my bill that much?
Yes. A constantly running toilet can waste thousands of gallons a month, which is often more than a slow slab leak.
Will my city adjust the bill for a leak?
Some Valley water providers offer a one-time leak adjustment once it's repaired. Ask your provider and keep the repair invoice.
Editorial note: this guide is general information for Phoenix-area homeowners, not a diagnosis. Conditions vary by home, so a licensed plumber should confirm the cause before any repair.