A SOURCE special section on regulation and control of water loss.
Importance of Customer Water Meter Accuracy
By Richard Relyea and Mark Carey
Customer meter accuracy is critical for monitoring and controlling distribution systems water losses.
THE AMERICAN WATER WORKS Association (AWWA) water audit (V5), defines apparent loss as “the nonphysical
losses that occur when water is successfully delivered to a water user but for various reasons is not measured or re-corded
accurately, thereby inducing a degree of error in the amount of actual customer consumption.” Apparent losses
are considered nonphysical losses in that no water is physically lost due to pipeline or equipment or operator failure.
Real losses are the physical losses of water from the distribution system including leakage and storage overflows—water
supplied to the system (System Input Volume) that never reaches the customer side of the meter.
AWWA manual M6 is the industry standard for meter selection and
installation, meter testing, and meter maintenance. It’s critical that
M6 be referenced when selecting meters for a water system system.
www.ca-nv-awwa.org 33
WATER LOSS CONTROL
Customer meter inaccuracy (defined
in AWWA manual M36: Water Audits and
Loss Control Programs as “the collective
under-registration of customer water
meters) is a subset of apparent losses and
can be very difficult to quantify. Although
meter age and the throughput volume
over the life of a meter were traditionally
thought to be the main factors in water
meter inaccuracy, proper meter typing
and sizing can have significant impacts.
Types of Meters
Historically, domestic water meters
were predominantly single jet, multiple
jet, oscillating piston and nutating disc
type meters. Designed to work under
severe conditions for long periods, these
mechanical meters have a tendency
to slow down and under-register over
time. Water quality impacts often result
in degradation to internal moving
parts, adversely affecting low flow
detection capabilities. Turbine meters,
typically used for large commercial users
including irrigation, fire service, and
large-scale metering, are less accurate at
low rates than positive displacement and
inferential jet-type meters. Compound
meters, developed to address the need
to accurately measure a wide range in
flow characteristics, basically include a
positive displacement (PD) meter and
a turbine meter. With many moving
parts, accuracy can degrade over time,
particularly without an active meter
maintenance and testing program.
U l t r a s o n i c ,
magnetic meters
and solid state/
smart meters and
related registers
were introduced
in the 2000s. They
have no moving
parts and rely
on either sound
waves, in the case
of ultrasonic me-ters,
or charged
electrons to mea-sure
voltage, in
order to indirect-ly
measure flows.
Since the cross-sec-tional
area of the
meter body is fixed
and has a known
value, water volume can be calculated
with high accuracy. Residential ultrason-ic
and magnetic type meters are capable
of measuring down to 0.01 gallons, or
0.001 cubic feet, and are relatively ac-curate
over a wide flow measurement
range, require little maintenance and
with no internal mechanical components
to wear out, have long lifespans.
Appropriate
meter typing is crit-ical
for minimizing
apparent losses. For
example, if a turbine
meter is placed on
a service that typ-ically
operates at
flows less than 4-5
gallons per minute
(GPM), or the facil-ity
once housed a
large-use customer
but the usage or cus-tomer
changed, the
low flow may not
be captured. These
losses are often mis-takenly
interpreted
as real losses and
can significantly
reduce overall revenues, creating billing
accuracies.
The relative accuracy of meters was
documented in a 2011 Water Research
Foundation (WRF) report, Accuracy of
In-Service Water Meters at Low and High
Flow Rates. Testing indicated that a 1
1/2-inch turbine meter does not actual-ly
start registering until the flow reaches