Water Meter Terminology Glossary

Following is a list of common terms used in water metering. Please contact us if you need assistance with industry terminology, meter sizing, meter typing, or installation questions.

5/8" Meter - A water meter with an internal measuring chamber flow capacity or "bore" of 5/8". the 5/8" designation does NOT refer to thread size. The original standard of a 5/8" meter was to attach to 1/2" plumbing and had a standard 1/2" AWWA meter thread to use 1/2" meter couplings. A 5/8" meter is also now referred to as a 5/8" x 1/2" meter. (5/8" flow capacity with 1/2" inlet and outlet). There is a newer meter that has the same 5/8" internal flow capacity and bore, but has 3/4" AWWA meter threads. It is referred to as a 5/8" x 3/4" meter. Internal components and registers of a 5/8" x 1/2 and 5/8" x 3/4" are normally the same and interchangeable, with the thread size being the only difference.
5/8" x 1/2" Meter - This is the 5/8" standard meter with 1/2" meter threads. 5/8" meter and 5/8" x 1/2" meter are used interchangeably. AWWA meter threads are straight meter threads used with a swivel coupling nut and meter gasket. Threads measure approximately 1.05" O.D. (3/4" NPS - not 1/2" NPT). The lay length is 7-1/2" end to end. a 5/8" meter uses couplings designated as 1/2" or 5/8" meter couplings This is a common size for older homes and older cities.
5/8" x 3/4" Meter - This is a 5/8" internal capacity meter but with threads designed for use with 3/4" meter service piping on inlet and outlet. The thread O.D. is approximately 1.25" (1" NPS - Not 3/4" NPT). The lay length is 7-1/2", the same as the 5/8" x 1/2" meter. It uses meter coupling designated as 3/4". This is currently the most common residential meter size.
3/4" (Standard) Meter - A standard 3/4" meter has a full 3/4" water flow capacity, or bore, and uses the same 3/4" AWWA meter threads as the 5/8" x 3/4" meter. However, the lay length is 9" inlet to outlet. It is normally used on 3/4" service lines where the full 3/4" flow capacity is required and can't be provided by a 5/8" x 3/4" meter.
3/4" (Short) Meter - This is a full 3/4" bore and measuring capacity meter, but with a 7-1/2" lay length. It is often used to upgrade a formerly 5/8" x 3/4" meter to full 3/4" without having to re-plumb for the longer 3/4" standard lay length, or where space is not available for the longer meter. Internal parts and registers are generally interchangeable with the standard 3/4" meter.
Absolute Encoder - An encoder register that outputs the exact position of the number wheels or digital count rather than an incremental pulse.
AMR - Automatic Meter Reading. Generally a technology for reading water meters in drive-by mode via a short distance ratio signal.
AMI - Automated Metering Infrastructure. A technology where a network of antennas, towers or other fixed infrastructure is installed to automatically collect meter reading at set increments via radio transmitted signals.
AWWA - American Water Works Association. An industry organization that sets North American standards in the public water supply industry for meters, valves, pipes, etc.
Check Valve - A valve that allows water to flow in only one direction. Similar to a non-return valve or backflow preventer.
Cold Water Meter - Unless otherwise designated as a HOT water meter, all meters should be consider as cold water meters for water at normal ambient temperatures. Manufacturer standards vary, but cold water can be considered to be 33F to 105F and sometimes up to 140F. Do not use a meter for hot water unless specifically designated for that use. See also Hot Water Meter.
Compound Meter - A compound meter is really a combination of two measuring technologies with a diverter check valve to switch between them. At low flow rates, water is diverted by a closed check valve into a low flow measuring element, usually PD or multi-jet. At high flow rates, the check valve opens and water is diverted to the turbine measuring element to measure high flow rates. Compound meters may have separate high and low use registers or combine reading into one with gearing. Compound meters are largely being replaced by newer Ultrasonic and Mag meters that are more accurate at all flow rates.
Digital Pulse - A pulse output that is in digital format vs an analog pulse. A digital pulse will have a very consistent voltage and frequency. An analog pulse may vary.
Drop-in Gasket - a gasket for oval/elliptical flange meters that can be dropped into place after the meter is loosely installed with the bolts.
Dry Contact Switch - A technology where the meter opens and closes a switch allowing a pulse of energy to pass where the switch device itself does not provide the power source.
Elliptical Flange - an oval shaped meter flange end or companion flange for 1-1/2" and 2" meters that has two bolt holes opposite each other.
Encoder - a meter register that sends the numerical reading directly out to a device in a coded format rather than a pulses that the external device has to count. A popular encoded output format is generically UI-1203 which was formerly and is sometimes still called the "Sensus protocol" as it was originally designed by Sensus company and provided to AWWA as a standard.
Encoded Output - Electronic Data output from an encoder type water meter register.
Extended Low Flow - a non-standardized measurement by a meter manufacturer of the lowest flow rate the meter can measure accurately. AWWA has standards for low, medium and high flow rates. Extended low flow would be how well a meter exceeds the low flow standards. Since there is no official standard, the rates and percentage claims may vary by manufacturer (Example: 1/4 GPM @ 95% accuracy)
Fire Meter - A meter normally installed on a building fire line to measure water used in a building fire sprinkler system.
Fire Hydrant Meter - A water meter that is generally 2" to 3" capacity for attachment to a fire hydrant nozzle to measure water used from a fire hydrant for construction, truck filling, or other non-emergency use.
Flange - The end of larger meters that uses bolts though holes rather than threads to attach the meter. Generally 1-1/2" and 2" meters can be purchased either threaded for meter couplings or flanged for flange installation. 1-/2" and 2" are generally oval or elliptical flanges with two bolts horizontally across from each other. 3" and larger are round flanges with 4 or more bolt holes evenly spaced around the flange.
Frost Bottom - A bottom on a meter that is designed to sacrificially break in the event of the expansion of frozen water. They are generally made of cast iron that will break before the more expensive brass body does.
Freeze Plate (same as Frost bottom)
Hot Water Meter - A meter specifically designed with components that can measure hot water heated by a water heater. Typically used when re-metering an apartment where one water heater heats multiple units or where hot and cold must be measured separately due to plumbing. Hot water meters will have a published temperature range starting at about 120F and higher. Do not use a meter not specifically marked for HOT water at temperatures above those rated by the manufacturer. Hot water meters often are colored red or have specific HOT markings.
Impeller - a horizontal turbine element like a paddle wheel that is used in single and multi-jet water meters.
Lay Length - The total length of a water meter from inlet to outlet. On threaded end meters, it is the end to end of the meter threads. On flanged meters it is the furthest distance from the outer side of the inlet and outlet flange. Lay length does not include space for the gasket thickness, but is the ACTUAL length of the meter inlet to outlet.
Lead-free (low lead, no lead) - This is a standard set by the US Government through the Safe Drinking Water Act for the amount of lead (metal) that can legally be used in plumbing products. The amount has changed over time. The most recent change took effect in January 2014 when the amount of allowable lead in a metal allow was reduced from 8% to 0.25%. Brass plumbing products installed after 2014 must be marked "lead-free", "low lead" or "no lead" and meet NSF-61G standards for lead testing and approval. Older unused products are NOT grandfathered in and cannot be installed. However, existing installed products may be used in their current places.
Lead Wire - Electronic registers will have a wire lead between the register and electronics. This may be referred to an encoder with a 6' wire lead. (This is not referring to the metal element but to a length of wire)
Low Flow - A minimum standard for accuracy at a specific rate set by the industry and AWWA. Typically the lowest acceptable rate of flow in gallons per minute. For PD meters, this is usually at +/- 1.5% accuracy (98.5% to 101.5% of actual)
Mag Meter (Electromagnetic Meter) - A meter that uses Faraday's law of physics to measure flow from two or more electrodes. The meters have no moving parts, but must have constant source of AC or DC power.
Main Case (Meter body, Casing)- The main body of a meter. For mechanical meters, this is generally the brass or iron outer case with threaded or flanged ends. Newer meters may also be stainless steel, plastic, or composite materials.
Maximum (intermittent) Flow - The highest flow rate that a meter can have in a short burst of time. This flow rate may be higher than the normal flow range top figure which is for maximum continuous flow.
Measuring Chamber - The internal mechanism that measures the water and transfers the reading by motion to the register. In the case of Positive Displacement meters it is the piston or disk and outer chamber. In multi-jet meters it is the impeller and casing, in compound meters is is the turbine. In ultrasonic or mag meters it is the area where the water flow is measured.
Meter Coupling - A fitting specifically designed to install threaded end water meters. The female end that attaches to the meter has a swivel nut with straight pipe threads. a gasket is inserted into the nut before securing. Never use thread sealant on the meter threads and swivel coupling nut. The sliding swivel nut acts as a union to remove the meter for repair or replacement. The other end of the meter coupling is a nipple or tailpiece generally of the size of the plumbing, and generally with male NPT pipe threads for permanent installation to the plumbing system with thread sealant.
Meter Threads - In the USA, water meters meet specifications of the American Water Works Association. AWWA has specific thread size standards for water meters that are NOT the same as tapered pipe threads (NPT). Meter threads do not provide a waterproof seal, but have a coupling nut go over them and compress a meter gasket against the face of the meter spud for the watertight seal. AWWA threads are not tapered like NPT threads, but are straight. they are also named based on internal sizes, not external, and are one size larger than NPS threads. (3/4" meter threads are actually 1" NPS/NPST) You do NOT use pipe sealant on meter threads.
MDM - Meter Data Management - Software in the billing office that takes reading and data logging data from meter readings and and does analysis for flow planning, water loss, conservation, and other needs.
MIU - Meter Interface Unit. Usually refers to a smart radio transmitter or external collection and communication device to store and forward readings for automated meter reading.
Multi-jet - An impeller based measuring technology where the impeller is housed in a case and multiple jets of water flow through multiple ports surrounding the impeller form all sides to distribute the flow evenly on the impeller from all directions.
New Meter Accuracy - An AWWA standard that generally requires a new meter to maintain a certain accuracy for a required period of time. Typically 5 years for residential meters.
Non-return valve - A small valve generally inserted into the inlet of a water meter so that water cannot flow backward. This is generally used to prevent meter reversal in the event of water backflow or failure of a backflow prevention device or check valve. They do not meet safety requirements of true backflow preventers, but just prevent water from surging back and forth through the meter.
Normal Flow Range - The expected, standard, and recommended flow range for a meter to operate at expected and acceptable accuracy. Using above or below the range may cause inaccuracy or damage to the meter.
Nutating Disk - Sometimes referred to a disk or disc meter, this is a PD measuring technology. There is normally a center ball with a flat round extension shaped similar to the planet Saturn with it's rings. The rings move around the center in an up and down factor as water pushes through.
NSF (NSF-61g) - National Science Foundation - NSF-61G is a standard for testing and approval of plumbing materials to be free of lead and other harmful contaminants for potable water.
Oscillating Piston - An oscillating piston is a PD measuring technolgy where a cylindrical piston rotates inside an enclosed chamber on a horizontal plane to measure water. Water pushes the piston around between entering and exiting.
Pulse Output - Electronic meter output in pulse format. for example a mete might generate one electronic pulse for every 10, 100, or 1000 gallons. The pulse can go to a remote register or an electronic device. The external device must be capable of counting the pulses and totaling them. Older remote meters often had an analog pulse put out by a generator register. Newer meters have a digital pulse put out by a battery operated device or a switched current (dry contact switch)
Positive Displacement - A water measurement technology where all water is measured by positively displacing a measuring element. In Theory, water cannot pass through the measuring chamber without moving the measuring element. Two common types are the Oscillating Piston and the Nutating Disc.
Remote Register - A secondary register normally wired to the meter installed register that can be installed a short distance away from the meter itself. Commonly mounted on an outside wall to read a meter in a basement or inside a building without having to enter.
Repaired Meter Accuracy - An AWWA standard that meters must meet if they have been repaired or are no longer new. Typically after 5 years once some wear or internal mineral deposits may have formed.
Reverse Flow - Flow of a meter in the direction not intended by the manufacturer. Most meters have an arrow for the correct direction of flow. Some meters will count backward when reversed, others won't. Reverse flow detection in smart meters can be use to determine improper installation, attempted meter tamper, failed check valves, and other anomalies.
Sensus Protocol (UI-1203) - A standard of data transfer from an encoded register to an external device such as a radio transmitter, electronic display, or touch pad. Adopted by AWWA as an industry standard.
Single Jet (Paddle wheel) - a meter that uses an offset impeller or paddle wheel to measure water. A single jet stream of water moves the wheel one online one side.
Spud - The threaded inlet or outlet end of a meter
Starting Flow - Starting flow is a relatively new term where a meter can start measuring water of any significance, although maybe not at high accuracy. Mechanical meters will require some pressure energy to move the physical measuring element such as an impeller or turbine.
Ultrasonic Meter (Transit Time, Dopler) - Ultrasonic meters use either Transit time or Dopler sound waves to measure the flow of water. They have no moving parts, but operate with transducers to measure the flow rate of the water and therefore the volume at a given velocity. They are very accurate, have no moving parts to wear, require no strainer, and can be installed in multiple configurations such as vertically where a PD meter cannot.
Register - The usually topmost part of a meter that keeps track of the numerical usage of the meter on a mechanical odometer or electronically on a solid state meter. It may also be an encoder or pulse register and send the reading out to an external device such as a counter, remote, touchpad, or radio MIU
Strainer - A strainer is a filter or screen that allows water to pass, but will catch objects and debris that could damage a meters internal components. Strainers may be a small screen on the inlet side of a meter, or a separate device installed prior to the meter. They are generally required for mechanical meter types such as PD, Multijet, Turbine, and Compound meters. They are not generally required for meters without moving parts such as Ultrasonic and Mag Meters.
Tamper Seal - a device to seal any removable parts of a meter to prevent tamper by those not authorized. Some may be proprietary screws, pins, or covers. some are simply wires threaded through holes in the screws or bolts and sealed with a tamper evident device.
Touch Read (Also touch pad, Read Pad, Touch remote) - a meter with a wire output to an external wire going to an inductive remote touch pad. A technology where a touch reader can send an inductive pulse into a touch pad and the meter replies with the an encoded meter reading. True touch is technically not required as the inductive signal can be up to 1/2" from the coil.
Turbine (Turbo) - Turbine meters have a propeller like device in the flow of water that moves with the water current and translates into the register for measurement.Turbine water meters are generally best for only larger meters 2" and larger and high consistent high flow rates. compound meters have a turbine measuring element for high flow rates, as well as another technology for low flow rates.
Wheels (encoder) (significant digits) - Most mechanical meters have a series of odometer wheels that move and increment water usage. Electronic meters have LCD numbers that simulate the same. A meter with 6 moving odometer wheels is referred to as a "6-wheel encoder". If only the last 4 wheels send out output electronically, it would be "4 wheel output". It refers to either the number of moving digits or number of significant digits used for billing.