Page 320 - Water Loss Control

Contr olling Real Losses in the Field—Pr oactive Leak Detection 289

communications (GSM) short message service (SMS). Several manufacturers
provide loggers able to transmit the recorded and logged flow and pressure values
on a regular basis using SMS. These loggers can transmit the data to a host computer
on a daily, weekly, or monthly basis. The cost of installation for this option is very
low. However, it is necessary to assess the cost for the SMS messages since this
service cost is set by the mobile phone provider in the local area. Dial up connections
using telephone lines or low power radio can be used as well for the transmission of
flow and pressure data. This option does not require power supply.
Manual data collection: Another option is to manually download the data recorded
by the logger on a regular basis depending on the intervals set up as economically
justifiable. This approach requires personnel to visit the DMA equipment on a
regular basis for data downloads. It has the advantage of frequent visual checks
on the equipment, but the disadvantage of high staff time required to make the
regular visits. This option involves the lowest installation costs since no automated
communication system is required, but the operational costs are high, since
ongoing staff and transportation costs are necessary.

16.6.6 DMA Data Analysis
The concept of DMA monitoring is to measure flow into a discrete area with a defined
boundary and observe typical variations in flow. The estimation of the real loss component
via minimum night flow analysis is carried out by subtracting an assessed or measured
volume of legitimate night consumption for each of the customers connected to the water
mains in the DMA. The minimum nighttime flow in urban areas usually occurs between
2:00 and 4:00 a.m. This flow value is the most meaningful data used in determining the leak-
age rate in the DMA. During this period, authorized consumption is at a minimum and,
therefore, leakage is at its maximum percentage of the total inflow. In regions where cus-
tomer landscape irrigation makes up a significant part of the demand during the minimum
nighttime flow period, the accuracy and the confidence in the calculated real loss figures
will diminish. The result obtained by subtracting the legitimate night consumption from the
minimum nighttime flow is known as the net night flow (NNF) and provides an estimation
of the volume of real losses during the MNF period. The leakage volume can be modulated
over the whole 24-hour period using the fixed and variable area discharge paths (FAVAD)
concept (see Chap. 18, or where we discuss the FAVAD principle).
NNF = MNF − legitimate nighttime consumption
The NNF is mostly composed of real losses from the distribution network and the
service connection piping between the water main and the customer meter. However, it
may also include leakage on the customer side of the meter and consumption through
unauthorized connections. Figure 16.18 shows the results of a MNF analysis.
Data for DMA Minimum Nighttime Flow (MNF) Analysis
In addition to the inflow measurements, pressure measurements at the zone inlet
point(s) and at the average zone pressure point the following data is also required to be
able to conduct a MNF analysis.
• Length of mains
• Number of service connections