A district metered area is a section of a water network with fixed boundaries and metered inflows, used to measure and track leakage.
A district metered area (DMA) is a part of a water distribution network that is cut off from the rest by closed boundary valves, so that all water entering or leaving it passes through a small number of flow meters. A DMA often holds about 500 to 3,000 connections, although sizes vary widely. Inflow meters, often with pressure loggers, record flow every 15 minutes or so. The key measure is the minimum night flow, usually seen between about 2 and 4 am, when customer use is lowest and leakage makes up a large share of the flow. Engineers subtract an estimate of legitimate night use to get night leakage, then compare it with past values and with other DMAs to decide where to send leak detection crews first. A simple example: a DMA has 1,200 properties and a minimum night flow of 9.0 m³/h. If legitimate night use is assumed to be 1.5 litres per property per hour, that is 1,200 × 1.5 = 1,800 L/h, or 1.8 m³/h. Night leakage is about 9.0 - 1.8 = 7.2 m³/h. A rise to 11 m³/h a month later would point to a new burst. To turn night leakage into daily leakage, engineers apply a night-day factor, because pressure, and so leakage, changes through the day. DMAs make leakage visible, help teams act fast on new bursts, and make pressure management easier. Limits: closing boundary valves can reduce fire flow, create dead ends with poorer water quality, and lower pressure at high points. Meters must be accurate, and a boundary valve left open by mistake gives wrong results. Setting up DMAs in an old network with poor records can take a lot of survey work. In intermittent supply, night-flow analysis is hard because pipes are not always full.