Page 154 - Water Loss Control

132 Cha pte r T e n

be carried out to remedy the specific causes of meter inaccuracy in the most economic
manner.
Loss of Accuracy Due to Mechanical Wear
Well-manufactured water meters can lose appreciable mechanical accuracy due to
• Aggressive water quality
• High rates of flow being measured
• Chemical or residual buildup
• Abrasive materials such as sand in suspension carried by the water
• Air running through the meter after a system outage
As the cumulative volume passed through the meter increases toward meter life
cycle levels then the mechanical failures are compounded. Chapter 16 provides detailed
information on the assessment of life cycle accuracy of customer meters and means to
control losses that occur in this subcomponent of apparent losses.
Zero Consumption Billings from Stopped Meters or Vacant Properties
Meters or meter-reading devices can fail to register for various reasons. However,
meters that show no registration might also reflect a customer property with no use,
such as that which may occur at a vacant property. Large numbers of customer meters
that mechanically fail to register any flow from billing cycle to billing cycle can account
for large volumes of apparent losses and uncaptured revenue.
Many water utilities employ the use of an estimated consumption volume if they
encounter periodic low or zero consumption volumes generated from meter reading.
This practice can be effective if the zero reads are only periodic. However, when estima-
tion is undertaken for many consecutive months, estimated volumes will likely deviate
from the actual consumption volumes. If all values of consumption for a given account
are based upon estimates for an entire audit year, then the volume assigned to that par-
ticular account for the water audit can be seriously in error. Water utilities should rou-
tinely review billing data and assess the occurrence of zero consumption bills,
particularly those that register zero consumption for several consecutive months. It is
worthwhile for the utility to dedicate personnel to physically inspect the meter site of a
representative sample of customer accounts to determine the reason for the continuing
zero consumption registrations. The findings of such inspections provide data that can
be used to model the occurrence of apparent loss in the zero consumption population
throughout the entire system.
By applying the above analysis, it is possible to model best case and worst case
scenarios for customer meter losses occurring due to meters registering zero consump-
tion. The best case reflects the overall accuracy of the entire meter population without
including zero consumption meters, a scenario that would occur only in the ideal case
of the water utility responding quickly to accounts registering zero consumption and
correcting meter or meter-reading problems just after they occur. The worst case reflects
customer meter population accuracy including the greatest potential extent of zero con-
sumption meters, reflecting a water utility policy that ignores zero consumption regis-
trations, allowing them to mount throughout the audit year. Calculate the apparent
losses in both the best and worst case, then the average meter accuracy can be calcu-
lated for water balance purposes, representing the average inherent accuracy of the