How can a water utility find evidence of hidden leaks?

A hidden pipe leak can release water without making an obvious puddle. A utility can begin with a water balance for a defined zone and time period. It measures water entering and accounts for water legitimately used, including known uses that are not recorded by customer meters. Changes in stored water must also be considered when they occur.

When incoming volume exceeds the accounted uses, the difference is a balance gap. Here 1,000 liters enter during one period, customer records account for 900 liters, and known unmetered uses account for another 40. With no change in stored water, 1,000 − 900 − 40 leaves a 60-liter gap. The periods must match: comparing today's supply with last week's use would create a misleading result.

Meter inaccuracies and recording problems can create apparent losses even when water reached a legitimate user. If meters are estimated to have underrecorded by 20 liters in this example, that explains 20 of the 60-liter gap and leaves 40 liters unexplained. The remainder is still not proof of a leak: it may include physical losses, unaccounted use and other data problems. Checking the measurements is part of investigating the water.

To add physical evidence, utility staff compare flows and listen for vibrations associated with water escaping under pressure. Sensors at different pipe locations can help narrow a suspected area, although pipe material and surrounding noise affect the signals. Combining accounting and field measurements gives a stronger explanation than either alone. The drawing does not identify or measure a real leak.