DESIGNER’S NOTEBOOK

Water-Meter Selection and Sizing

Timothy A. Smith, CPD

A recent announcement from the

Figure 1. Descriptive Specifications for Four Types of Water Meters
Chicago Department of Water prompt-
ed me to think about an aspect of Disc Meter
plumbing design that may be taken A. Positive displacement type AWWA C700-02 and/or C710-02 (cast bronze body C700-02/ plastic
body C710-02)
for granted. The news is that the City
1. (Bronze) or (plastic) body constructed with a nutating disc or oscillating piston; flanged or
of Chicago will undertake the major threaded connections
expense of installing water meters in B. Application: Residential and small commercial buildings with flush tank toilets or small quantity
all houses in the city. Evidently, there of flush valves
are thousands of houses in Chicago C. Commentary: Available in sizes 1/2-in. through 2-in.; 1/4-gpm minimum through 160-gpm
that have never been metered. The peak flow; available with analog/digital remote reading capability; accurate low flow range; pres-
residents have been charged for water sure loss increases with flow somewhat proportionally to the recording inaccuracies.
usage, but the charge was based on Turbine Meter
an estimate rather than on actual use. A. Turbine type, AWWA C701-02
Someone now has figured out that the 1. Bronze body with rotating impeller (rotar) located within the measuring chamber mounted in
initial water-meter installation cost will the center of the flow; vortex reducing flow vanes; flanged connections
be offset by the additional revenue. B. Application: Commercial, process systems, large institutional, and facilities of potentially high
usage and high flow rates
The concern is that many engineers
C. Commentary: Available in sizes 2-in. through 20-in.; 2 1/2-gpm minimum through 19,000-gpm
who design water systems connected continuous; remote reading is available; small fluctuation in accuracy throughout entire flow
to municipal water supply may take range; inaccurate for flows less than 2 gpm.
water-meter selection and sizing for Compound Meter
granted. Regularly, municipal water A. Combination type, AWWA C702-01
purveyors dictate the type, size, and 1. Bronze body with dual measuring chambers separated by a pressure/velocity-sensitive
cost of the water meter to be used for mechanism or plate; positive displacement chamber and turbine chamber combination; as
buildings. This practice has become pressure loss through positive displacement (low-flow) chamber increases, the mechanism
more prominent with the advent of or diverting plate shifts the flow to the turbine (high-flow) chamber; flanged connections
remote meter reading and digital con- B. Application: Commercial, institutional, places of assembly, and facilities with fluctuating usage
nectivity. It is very common for a and flow rates
municipality to read a water meter C. Commentary: Available in sizes 2-in. through 6-in.; 1/4-gpm minimum through 1,200-gpm peak
flow; available with analog/digital remote reading capability; accurate low and high (peak) flow
through the telephone system. This is
range; progressing pressure loss until mid-flow range when low-flow chamber diverts to the
easy to do, even with yesterday’s tech- high-flow chamber with lower pressure drop; can experience quick pressure-loss spike when
nology. Many designers have become switching from low-flow to high-flow chambers.
familiar with the size and type of water Propeller Meter
meter that the water purveyor provides A. Propeller type, AWWA C704-02
for a certain building type. Therefore, 1. Iron or fabricated steel body and thermoplastic impeller with deep impeller vanes, curved
they can establish the amount of pres- and tapered (similar to a propeller) for reduced resistancy; mounted in open pipe with wafer
sure loss to apply to the pipe-distribu- or lug connections
tion sizing calculations from the meter B. Application: Process or industrial facilities, well-pump discharge, pumping stations or sewage
manufacturer’s pressure loss curves. treatment plants where flow rates are very high and constant
What about installations where the C. Commentary: Available in sizes 2-in. through 72-in.; 30-gpm minimum through 50,000-gpm
plumbing contractor is required to continuous; unable to accurately register low and intermittent flows; broader band of inaccuracy;
exceptional for high, continuous flow applications.
provide the water meter based on the
designer’s plans and specifications? A
water meter typically is located at the
water service entrance to a building. plumbing design, such as tenant sec- Sizing Is Critical
Therefore, it is the first device calcu- ondary metering, control of the appli- My last article, on tempered water
lated into a water-distribution system cation rate in irrigation systems, meas- systems, outlined the false concept of
design that inevitably results in having urement of water usage or loss for matching the mixing valve’s inlet sizes
the proper flow and pressure at the process or boiler systems, and control with the pipe sizes. The same princi-
farthest fixture in the building. Water of the regeneration cycles for water ples apply to water-meter sizing,
meters have other applications in softeners, to name just a few. although the system’s dynamics are

70 Plumbing Systems & Design • Jul/Aug 2003

 DESIGNER’S NOTEBOOK
supply by backflow or
back siphonage. In addi-
tion to being uneconomi-
cal, oversized water
meters typically do not
accurately measure mini-
mal flow rates. Larger
meters are more expen-
sive than smaller meters.
Municipalities usually
assess meter and tap fees
according to size, so
oversizing can become
expensive for a building’s
owner.
When selecting and
specifying a domestic
water meter for a build-
ing’s service entrance, you
must understand the
building’s size, function,
fixture types, usage occu-
pancy, and peak popula-
tion. These factors will
allow you to determine
the minimum and maxi-
mum flow rates and
enable you to select the
proper water meter, based
on pressure loss, record-
ing accuracy, and capabili-
ty of accommodating the
projected flow variations.
The ASPE Data Books pro-
vide good resources for
calculating the building’s
water usage. Remember to
always specify tapered fit-
tings when reducing or
increasing from the meter
size to calculated pipe
sizes. The alternative
reducing/increasing
more forgiving of an improperly sized and noise. High-pressure losses method using pipe bushings can pro-
water meter than an improperly sized through meters at peak flow rates can duce three to ten times the pressure
three-way mixing valve. Remember, result in pressure surges, water ham- loss of tapered fittings, depending on
using the one-size, one-type-fits-all mering, and the inability to maintain size.
philosophy is really asking for trouble. proper residual pressure at the fixtures
Improperly sized water meters can or equipment. High-pressure loss
Meter Types
The American Water Works
affect the operation of the building’s through a meter also corresponds
Association (AWWA) has promulgated
water distribution system and plumb- with a high-flow velocity and thus
widely recognized and accepted stan-
ing fixtures, which also can affect the results in more noise. Improperly
dards for the construction of water
health of the building’s occupants. sized meters can cause negative pres-
meters. All water meters manufactured
Undersized water meters can cause sures in the piping system and lead to
excessive pressure loss, reduced flow, contamination of the potable water continued on page 72

Jul/Aug 2003 • Plumbing Systems & Design 71

 DESIGNER’S NOTEBOOK
Figure 2. Typical Accuracy and Performance Graphs

Courtesy of Badger Meter, Inc.

for domestic water service use in the critical. Process applications may only the pressure loss at the meter, the less
United States are manufactured in require approximate flow recording. pressure is available for the system’s
accordance with AWWA standards. Positive displacement meters are the friction loss. Thus, larger pipe sizes
These standards set forth construction best selection for small commercial or are required downstream of the
criteria, physical construction, internal institutional facilities or residences. undersized meter. If a backflow pre-
components, dimensions, and testing They have excellent accuracy at low venter is required on the service (typi-
criteria to help ensure uniformity flows and, if sized properly, can accu- cally consuming 5–10 psi), it is neces-
across the industry. All water-meter rately measure the peak flow rates. sary to be more conservative with the
manufacturers that meet the AWWA Compound meters (see Figure 3) are water-meter pressure-loss selection.
standards can provide the test results an excellent choice for large commer- It is recommended that the calculat-
for their products. The designer cial or institutional facilities because ed peak flow rate for the facility not
should maintain a water meter prod- they have the ability to accurately exceed 80% of the maximum capacity
uct binder with pressure-loss curves accommodate low flows and high of the meter. This recommendation
and accuracy graphs, produced in flows through their multiple-measur- needs to be evaluated closely when
accordance with AWWA standards for ing chamber design. Refer to Figure 2 low incoming residual pressures are
each meter type and size. for performance curves for a typical prevalent or backflow preventers are
Figure 1 lists descriptive specifica- compound-type meter. Turbine and required. It is not uncommon to
tions for various types of propeller meters are design for a maximum of 2–3 psi
water meters utilized for If the meter is better suited for contin- pressure loss through the water meter
domestic water applications. uous, higher-flow appli- where municipal water pressures are
Table 1, Table 2, and
to be used for cations and are inaccu- weak.
Table 3 are reprints from billing purposes, rate at low flows. Strainers
AWWA Standard M22, as accuracy Turbine and propeller Water meters have internal mechani-
reprinted in ASPE Data Book meters are not recom-
is critical. cal components that move with the
Volume 2, Chapter 5. These mended for commer- flow of water, so it stands to reason
tables will provide additional cial, institutional, or res- that debris and sediment will have an
guidelines for selecting and idential buildings adverse effect on the meter’s opera-
sizing water meters, but the manufac- because the flow rates are constantly tion. It is recommended that an in-line
turers of water meters can supply test fluctuating and minimum flow rates strainer on the meter’s inlet be speci-
curves of each meter type and size may be as low as 1/2–2 gpm. fied to collect debris and sediment
that better define actual performance After the meter type is selected, a and prevent them from entering the
and characteristics. See Figure 2 for size needs to be determined. The size meter body. Strainers are available
typical performance and accuracy is established by comparing the mini- that are designed specifically for use
graphs. mum and peak flow rates of the facili- in conjunction with water meters.
Meter Selection ty against the minimum and maximum These strainers are designed and engi-
The first step in selecting a meter is flow capabilities of the meter size. neered to provide low pressure losses.
to establish the purpose for metering The flow rate will correspond to a They also have removable screens
the service. If the meter is to be used pressure loss, which factors into the and accessible covers to facilitate
for billing purposes, accuracy is pipe-sizing calculations. The greater cleaning and maintenance. Strainer

72 Plumbing Systems & Design • Jul/Aug 2003

 DESIGNER’S NOTEBOOK
Figure 3. Three Types of Water Meters

Compound Meter
Disc Meter

Turbine Meter
Courtesy of Badger Meter, Inc.

maintenance is critical because a or vaults. I do not recommend this and pressure loss. Accuracy is critical
clogged or dirty strainer impedes flow installation. It makes the meter hard to the purveyor of water because
and increases pressure losses. to maintain and service, and exterior meters that inaccurately measure the
Installation pits and vaults can flood. In some supply result in lost revenue. Pressure
The installer needs to strictly follow cases, submerging the water meters loss is critical to designers because
the manufacturer’s installation instruc- causes rapid deterioration and corro- they need to ensure that their engi-
tions. Improper installation may affect sion to the unit. Also, there is a neered systems operate properly. ■
the meter’s operation, capability, and remote possibility that the contami-
accuracy. Meters should be located in nated water in the pit can leech into
an accessible location and protected the potable water supply.
from damage. Meters are mechanical It is recommended that a floor drain
devices that need periodic testing be installed adjacent to the water Tim Smith is vice presi-
and repair. Make sure there is ample meter, especially for larger meters. The dent, partner, and found-
floor drain can reduce or eliminate ing member of Metro
room to repair or remove the unit.
water damage to the building caused Design Associates, Inc., in
Envision what it would take to work Schaumburg, IL. He has
on the unit. Refrain from installing by meter repairs, replacement, or test-
more than 23 years expe-
meters in crawl spaces, under stairs, ing. Larger meters are tested in place, rience covering all aspects of consulting
or in confined spaces. so it is imperative to have somewhere engineering, specializing in plumbing, fire
Some areas still allow the installa- to discharge the test water. protection, and civil engineering. His e-
tion of water meters in exterior pits The bottom line is meter accuracy mail address is tsmith@metrodgn.com.

Jul/Aug 2003 • Plumbing Systems & Design 73