An unchanged display is not the same as zero water use
A water meter can show no change during a short check because the volume is smaller than a display increment, because the display has not refreshed, or because the use is intermittent. Read the meter's units, smallest displayed increment and refresh behavior before turning two readings into a small-leak estimate. None of those display properties, by itself, establishes the meter's low-flow accuracy.
This guide adds a resolution check to a no-use observation. It does not locate a leak or specify the accuracy of an unidentified meter. All numerical observations below are invented examples; no property or meter was tested.
Keep billing units, display resolution and response time separate
Bellevue Utilities' meter explanation describes electronic registers displaying down to 0.001 cubic foot, with an update interval of 32 seconds. It distinguishes those readings from billing in CCF, or hundreds of cubic feet. Its FLOW indicator can also lag a change in use. These details describe the meters in that utility guidance, not every meter installed in the United States.
Using the utility's rounded conversion of 7.48 US gallons per cubic foot, one 0.001-cubic-foot display increment represents approximately 0.00748 gallon. One CCF represents approximately 748 gallons. Copying only whole CCF values from a bill would discard the finer information needed for a short observation.
| Property | Question to answer | Wrong substitution |
|---|---|---|
| Register unit | Gallons, cubic feet or another unit? | Assuming every number is gallons |
| Displayed increment | What is the smallest readable change? | Calling it the meter's accuracy |
| Refresh behavior | When does the display show a new value? | Treating a stale value as a fresh measurement |
| Low-flow registration | What does the exact meter document? | Inferring it from the number of decimal places |
Calculate a display-only uncertainty bound
For an illustrative register that rounds each cumulative reading to the nearest increment d, each displayed endpoint differs from its underlying registered value by at most d/2. Subtracting two endpoints can therefore introduce up to d of difference error. For an interval lasting T hours, the resulting display-only rate bound is d/T. This is an original rounding model, not a specification for the Bellevue equipment.
Suppose a register with d = 0.1 gallon changes by 0.2 gallon over two hours. The displayed average is 0.1 gallon per hour. Under the stated rounding assumption, the registered change could lie between 0.1 and 0.3 gallon, so the corresponding average lies between 0.05 and 0.15 gallon per hour. Those limits exclude calibration error, timing error, missed low-flow registration and unwanted water use during the interval.
| Same hypothetical 0.1-gallon increment | Interval | Display-only rate bound |
|---|---|---|
| Two endpoint readings | 0.5 hour | ±0.20 gal/hour |
| Two endpoint readings | 2 hours | ±0.05 gal/hour |
| Two endpoint readings | 4 hours | ±0.025 gal/hour |
A longer valid interval reduces this particular rounding effect. It does not guarantee a better leak diagnosis: an automatic appliance may start, a leak may stop, or occupancy may make a no-use interval impossible. Do not extend a short measured rate to a month without a separate assumption about persistence.
Record a result that another person can interpret
Save the meter identifier, utility instructions, complete start and end readings, their units, observation times and any refresh delay. Record whether automatic water users were excluded. If the display never changed, write “no displayed change during this interval,” rather than “no leak.” If the meter's rounding or registration behavior is unknown, leave the numerical uncertainty bound unspecified.
Use our leak and meter guide to separate a supply-wide reading from a toilet dye test. The toilet research page concerns flush volumes, which cannot supply a missing leak-rate measurement. The next useful action is a better-defined observation or utility clarification, not extra decimal places on an unsupported result.