MNFs and DMAs – New Concepts?
Iāve read a lot of papers about water loss reduction. Two concepts that show up frequently are Minimum Nighttime Flow (MNF) and District Metered Areas (DMA). DMAs are areas in the distribution system that can be isolated such that all system inflows and outflows (not including customer use) are metered. They are helpful in identifying areas where leakage is prevalent. Most of the time, leakage is a small fraction flow, and it is difficult to identify a small/medium leak in a DMA. For example, recognizing a 10 gpm leak in a DMA with a 200 gpm average flow is easier than finding one when the demand is 20,0000 gpm. However, in the middle of the night, water use in DMAs decreases and leakage becomes a more easily identifiable portion of the flow. The flow at this time is referred to as the MNF and it is usually measured at an hour somewhere between 1 a.m. and 5 a.m. If the MNF is less than or about 50% of the average daily flow, that DMA is not considered a likely source of major leakage. If it is higher and if it changes fairly suddenly, thatās a good place to look for