How this calculation works
Read the same meter twice, subtract known use and divide by elapsed time. The remaining rate is unexplained use, not a confirmed leak; bill projection applies entered tiers to base use plus extra volume.
Unexplained L/hour = ((end m³ − start m³) × 1,000 − known litres) / elapsed hoursA worked example
An 0.08 m³ increase over eight hours with no known use is 10 L/hour. At that continuous rate, 30 days adds 7.2 m³; the example cumulative tariff increases the bill by 166 currency units.
Good to know
Diagnostic arithmetic only; no leak location or repair diagnosis. Assumes a continuous repeated rate. Fixed charges, sewer fees, tax, rollover and meter accuracy beyond display resolution are excluded.
Reference: US EPA WaterSense: leaks and water use (opens in a new tab) ↗
A residual is not automatically a leak
Toilets, appliances, storage filling and forgotten normal use can appear in a meter difference. Enter known interval use explicitly rather than labeling the full change as leakage.
The tool reports unexplained use because two readings do not establish where water went. Repeat or investigate the measurement as appropriate; the arithmetic alone cannot identify a fault or a repair.
The ro water recovery and running cost calculator adds measure RO recovery from simultaneous product and reject collections, then estimate daily feed, reject, active runtime and entered water-plus-power cost.
Display resolution creates a range
If each reading is rounded to the nearest display increment, the difference can be off by up to one full increment. Dividing that volume by test duration gives a resolution-only rate bound.
This is not a statistical confidence interval and does not cover every meter error. The lower unexplained rate is clipped at zero; a short test on a coarse meter can have a wide range relative to the estimate.
Bill extra water at the marginal tiers
Cumulative thresholds define how much usage falls in each price band. The incremental bill is the bill with projected extra water minus the bill for the other entered use.
This differs from multiplying extra volume by the first tariff rate. Enter the final unlimited tier with ceiling zero. The example rates are illustrations, not a fetched municipal tariff.
Use the result with the next measurement
The RO water recovery and running cost calculator gives a way to estimate a purifier’s measured feed demand. If it operated during the meter test, include its total feed use rather than only the drinking-water output as known usage.
Diagnostic arithmetic only; no leak location or repair diagnosis. Assumes a continuous repeated rate. Fixed charges, sewer fees, tax, rollover and meter accuracy beyond display resolution are excluded.
A few questions, answered
Does positive unexplained use prove a leak?
No, unrecorded normal use and measurement effects may explain it.
Are tariff ceilings cumulative?
Yes; the final zero ceiling denotes the unlimited tier.
Are charges official local rates?
No, enter your current applicable tariff.