Page 321 - Water Loss Control

290 Cha pte r S i x tee n

60 30
Pressure
50 25
40 20
Flow rate 30 15 Pressure

20 Minimum night Varying customer use 10
consumption
Minimum Net night
10 night flow Burst leakage 5
flow
(leakage) Background leakage
0 0
00:00 02:00 04:00 06:00 08:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00

FIGURE 16.18 Twenty-four-hour leakage modeling based on minimum night fl ow analysis.
(Source: IWA Water Loss Task Force.)

• Number of household properties
• Number and types of nonhousehold properties
• Legitimate nighttime consumption (can be estimated or obtained by measuring
a sample of customers and inferring for the entire population, or measuring the
entire customer consumption by a fixed network AMR system)
Legitimate nighttime consumption is generally composed of three elements:

• Exceptional night use: Some public, commercial, industrial, and agricultural
customers will have significant water use during the nighttime period due to
the nature of their business processes. Such uses can be large in relation to the
minimum night flow into the zone. These customers have to be identified
through discussions with local operational staff and analysis of consumption
data from the billing system. Where a customer in a zone is thought to have a
significant night use, consumption readings or recordings of this customer need
to be taken during the MNF measurement in order to accurately deduct this
component of legitimate consumption from the total inflow.
• Nonhousehold night use: Nonhousehold customers who are not identified as exceptional
night users may, nevertheless, consume some water at night, for example, in automatic
flushing urinals. Some allowance for this night consumption has to be made. This is
often accomplished by making estimates based upon the type of industry and typical
published consumption volumes for such users. Where necessary, this data can be
supplemented by local short-term data-logging of specific customer meters.
• Household night use: Household or residential customers also consume some water
during the minimum nighttime flow period. Consumption occurs due to toilet
flushing, automatic washing machines, time-programmed dishwashers, and
outdoor landscape irrigation. Ideally, night customer consumption measurements
of typical household customers can be gathered for the proposed DMA in order
to determine an appropriate level of household night water consumption to