Start with the bill itself
Fullerton bills for water through its own city utility, so your usage history comes from the city's meter readings. Before looking for a leak, compare the latest bill with the same period last year and with the months just before. Check the number of days in the billing period and the units of water used, not just the dollar total, since rates and charges can change.
If usage really did rise and nothing in your household changed, such as guests, a new pool fill or a new lawn, it is time to look for water going somewhere you cannot see.
Work from easiest to hardest
- 5 minutes
- Compare usage units with previous bills and confirm the billing period length.
- 15 minutes
- Run the meter test with every fixture, appliance and the sprinkler controller off.
- 15 minutes
- Put food coloring in each toilet tank and check the bowls after 15 minutes without flushing.
- 30 minutes
- Review the irrigation controller schedule and run each zone while watching for broken heads.
- 30 minutes
- Close the house shutoff and the water heater cold inlet in turn, watching the meter after each.
- Next
- If the meter still moves and the cause is not found, call a licensed plumber for leak detection.
Likely causes and how they show up
| Cause | Meter behavior | Other clues |
|---|---|---|
| Leaking toilet flapper | Slow, steady or intermittent movement | Tank refills on its own, dye shows in bowl |
| Irrigation leak or stuck valve | Moves even with the house shutoff closed | Soggy lawn strip, water at a valve box |
| Service line leak | Moves with the house shutoff closed | Wet area between the meter and the house |
| Hot water line under slab | Stops when the heater cold inlet is closed | Warm floor, heater running often |
| Cold line under slab or in a wall | Moves with heater inlet closed, stops at house shutoff | Damp floors or walls, sound of water |
| Changed usage | Still when everything is off | Guests, new landscaping, pool top-ups |
Keep a record while you investigate
- Copies of the last 12 months of bills.
- Dated photos of meter readings before and after each test.
- Notes on which valve stopped the meter, if any.
- Photos of any wet areas, stains or warm spots.
- The plumber's written findings and invoice after repair.
Example: a bill that doubled over summer
Illustrative example. Not a real job or customer.
A homeowner sees usage roughly double from one bill to the next. Nothing inside the house seems wet and no one hears running water.
- The meter moves with everything off.
- Closing the house shutoff does not stop it.
- Turning off the irrigation backflow valve stops the movement.
- A walk along the sprinkler lines finds a soggy strip near one valve box.
The leak was on the irrigation side, not inside the house. A sprinkler line repair, not slab leak detection, was the right next step.
Common questions
How much can a hidden leak add to a bill?
It depends entirely on the leak's size and how long it runs. The meter test shows whether there is one; a plumber can then judge its size and location.
Can the city check for a leak for me?
Ask the city's water utility what it offers. It can usually confirm reading history, but locating a leak on your side of the meter is typically the owner's job.
What if the meter is still but the bill is high?
Then the extra water was probably used, not leaked. Review irrigation schedules, pool fills and household changes, and ask the city to verify the reading.
General information for Fullerton, not a quote or professional advice. In an emergency, call 911.