Page 261 - Water Loss Control

234 Cha pte r F o u r tee n

often base the estimate on the recent trend of customer consumption, or they may use
another method. If a poor or outdated estimation algorithm exists in the customer bill-
ing system, underestimation or overestimation of customer consumption can occur,
either of which could distort consumption data needed for operational purposes. The
water auditor should come to understand the method used to estimate consumption
and consider programming refinements if it is determined that the existing method cre-
ates inaccuracies. A quantity representing the amount of missed customer consumption
due to this occurrence should be included in the water audit.
A significant type of error can occur in the way that billing adjustments affect regis-
tered consumption data. An important question: are billing adjustments triggered by
modifying actual consumption volumes? As described in Sec. 14.2, billing systems
designed with good revenue collection intention may corrupt the operational integrity
of customer consumption volumes when generating a credit.
Distortions in customer consumption due to billing adjustments can occur when billing
systems do not distinguish between registered consumption (from meter readings) and billed
consumption, listed on the customer bill and archived in the billing records. Billed con-
sumption can differ from registered consumption when the customer is due a monetary
credit. If the billing system creates the credit (negative revenue to the utility) by creating
negative consumption values, actual consumption data becomes distorted. Billing systems
that include separate fields for registered and billed consumption avoid this problem.
Table 14.4 gives an example of a residential customer account that incurred esti-
mates for a 23-month period, during which time the property was temporarily vacant
and then sold to a new owner who consumes less water than his predecessors. Begin-
ning in October 2002 the water utility was unable to obtain a reliable meter reading at
this property. This may have been due to blocked access to the meter, a failure of AMR
equipment or another cause. Unfortunately, the water utility was unable to correct this
condition and obtain an accurate meter reading until August 2004. During the period
without readings, the water utility assigned an estimate of the consumption based upon
the customer’s recent history, in this case 885 cubic feet/month.
This estimate, shown in Column D, closely matched the actual consumption (shown
in Column G for illustrative purposes) until April 2003, when the property was vacated
and placed for sale. The property was vacant until August 2003 and experienced only
minimal water consumption during periodic caretaker visits from April to August 2003.
Upon sale to a new owner in August 2003, a regular pattern of water consumption
resumed, but at a slightly lower rate than the previous owner.
Between April 2003 and August 2004 (17 months) the assigned estimate (885 cubic
feet) notably overestimated the consumption for this account. When the water utility
was once again able to gain an accurate meter reading, it found that its estimate of the
July 2004 meter reading (42477) was overstated by a total of 4132 cubic feet, since the
last accurate meter reading in September 2002. This resulting cumulative overestima-
tion error was compounded by

• The lengthy duration (23 months) of the period with no meter readings
• The 4-month period of vacancy of the property
• The lower water consumption habits of the new property owner

Upon obtaining an accurate meter reading in August 2004 an adjustment of nega-
tive 4132 cubic feet was necessary and a credit due to the customer in the dollar amount
commensurate with the volume of adjusted consumption.