First prove that water is moving when every intended use is off. Then isolate branches and fixtures, measure the remaining flow and repeat the same test after repair.
1. Confirm unexplained flow at the meter
Choose a period when nobody needs water. Turn off taps, irrigation, appliances, treatment backwash and automatic tank filling, but do not disable equipment that must remain on for safety. Record the complete meter reading or photograph it.
Wait two hours without intended water use and read the meter again. Any change strongly suggests a leak or an overlooked automatic demand. On a private well, a pressure drop or unexpected pump cycling can serve as a clue, but it is not a direct volume measurement.
- Tell everyone in the home that the test has started.
- Record the meter reading and the exact start time.
- Keep all known water uses off for two hours.
- Record the end reading and list any equipment that ran.
2. Isolate fixtures and branches
Start with toilets, outdoor taps, irrigation, water-treatment drains, humidifiers, ice makers and storage-tank overflows. Close accessible fixture isolation valves one at a time and watch whether the meter or leak indicator stops.
A silent toilet leak may pass from the tank to the bowl without making a puddle. EPA WaterSense recommends adding a few drops of food colouring to the tank and checking the bowl after 10 minutes; flush immediately afterward to avoid staining.
US EPA WaterSense — Home maintenance ↗3. Measure the leak, not just the symptom
For a visible drip or discharge, collect water for a measured number of seconds and convert the volume to litres per minute. For a hidden leak, subtract two meter readings and divide by the elapsed minutes.
Decide whether the flow is continuous or intermittent. A 0.25 L/min leak that runs all day is very different from a valve that leaks for 15 minutes after each cycle. Enter both flow and active hours in the calculator.
4. Repair, repeat and keep a baseline
After repair, repeat the same no-use test for the same duration. A stable meter is better evidence than a dry surface alone. Record the date, starting and ending readings, repair made and remaining unexplained flow.
Stop and use a qualified plumber or leak-detection specialist if isolation cannot locate continuous flow, if a buried service line may be leaking, or if opening equipment could expose electricity, pressure, hot water or contamination hazards.
What each observation can tell you
| Observation | Likely meaning | Next check |
|---|---|---|
| Meter moves with all known use off | Leak or overlooked automatic demand | List and isolate branches |
| Meter stops when one valve closes | Fault is downstream of that valve | Inspect fixtures on that branch |
| Colour appears in toilet bowl | Tank is leaking into the bowl | Inspect flapper, seal and fill level |
| Pump cycles with no demand | Pressure is escaping or controls are faulty | Check pressure side and pump controls |
Worked example
Convert a meter change into leak flow
With all intended use off, the meter rises from 128.420 m³ to 128.450 m³ in two hours.
Volume change = 0.030 m³ = 30 L Elapsed time = 120 min Leak flow = 30 / 120 = 0.25 L/min Daily loss if continuous = 0.25 × 60 × 24 = 360 L/day
Use 0.25 L/min and 24 h/day in the leak-loss calculator, then repeat the meter test after repair.
What to have ready
- Readable water meter or a measured collection container
- A no-use test window agreed with everyone in the home
- Automatic water users identified before the test
- Accessible isolation valves labelled by branch or fixture
- Start and finish readings, times and repair notes recorded
Common mistakes
- Running a meter test while an appliance, irrigation zone or treatment cycle is active.
- Assuming no puddle means no leak.
- Using a short observation for a slow or intermittent fault.
- Estimating cost without including wastewater charges billed from metered water.
- Opening pressurised, hot or electrical equipment without safe isolation.
Reference check: 5 September 2026. Sources include US public agencies. Principles are general; regulations and design values must be checked where you live.Worked examples use stated hypothetical inputs.