Page 91 - Water Loss Control

Validation of Sour ce Meter Accuracy 73

maintain the function and accuracy of those meters serving as source meters. In many
ways, the reliability of the entire water audit is only as good as the source meter man-
agement is in a water utility.

6.5 What to Do if Meters Do Not Exist at Key Metering Sites
Perhaps one or more water sources are unmetered, or have meters that are not routinely
monitored. In such cases the following applies:
If no meters exist at a water source: Use a portable meter or estimate the flow.
Portable meters can be insertion types or strap-on types and can be installed on
source piping just downstream of the treatment plant effluent or other source.
A minimum of 24 hours of continuous metering should be obtained. If portable
metering is not feasible, one way to infer an estimate is to utilize treated effluent
water-pumping records. If the water pump performance characteristics are
known, a volume estimate can be derived by multiplying the number of hours
that the pump was operated during the year by the average pumping rate. If
water is taken from a large reservoir, an estimate of the withdrawal can be
formulated by accounting for the amount of drawdown of the reservoir level,
adjusted by the amount of inflow from streams and rainfall. Such methods give
an approximate volume measurement, and unmetered sources should ultimately
be designated for metering when possible.
If source water meters have not been routinely monitored: Conduct an inspection of
the source structures and meter. Note the type of metering device that exists
(e.g., venturi flowmeter, magnetic flowmeter, ultrasonic flowmeter). Note basic
information about the measuring device: type, identification number, frequency
of reading, type of recording register, unit of measure (and conversion factor, if
necessary), multiplier, date of installation, size of pipe or conduit, frequency of
testing, and date of last calibration. Document this information as in Table 6.4.
Attempt to obtain a record of how much water was produced by each source during
the period of the audit. Most meters have some type of register, or totaling device. Reg-
isters may be round reading or direct reading. Round-reading registers have a series of
small dials with pointers, registering cubic feet, or gallons, in tens, hundreds, thou-
sands, and ten thousands. Direct-reading registers have a large sweep hand for testing
and a direct-reading dial that shows total units of volume. If the meter has not been
routinely read, tested, or calibrated, efforts should be initiated to calibrate the meter
and institute routine reading or polling of the meter. Many drinking water utilities now
link source meters with SCADA systems that convey data in real time to centralized
computers, where the flow data is totaled and archived for easy retrieval. Again, a por-
table meter can be utilized to obtain measurements to compare during any source meter
calibration or verification activities.

6.6 Summary: Source Meter Accuracy
Source meters register the bulk water resource supply to the water utility, as well as
interconnection transfers between water utilities, major treated water transmission
flows into and out of tanks and other storages, and flows across pressure zones and