| Positive displacement (piston or nutating disc) | Water fills and empties measuring chambers. The movement of a piston or disc is counted to calculate the volume passing through the meter. | Homes and other small connections with relatively low flow rates. | Can measure low flows well; works without an external power supply in many mechanical configurations. | Moving parts can wear or be affected by debris and scale. Check the meter’s flow range and strainer requirements. |
| Multi-jet or single-jet | One or more water jets turn an impeller. Its rotation is converted into a volume reading. | Small residential and light commercial service, depending on the model and local requirements. | Compact design and straightforward mechanical operation; many models do not need external power. | Impeller meters have moving parts. Water quality, installation orientation, and the specified flow range can affect performance. |
| Turbine or Woltmann | Flow turns a rotor aligned with the water stream; rotor speed is used to determine the flow volume. | Larger pipes and applications with sustained, relatively high flow, such as some building or irrigation systems. | Well suited to higher flow rates when correctly sized and installed. | May be less suitable for very low flows. Moving parts and flow disturbances can affect readings; follow the manufacturer’s straight-pipe and installation guidance. |
| Compound | Combines a smaller meter for low flows with a larger meter for high flows. A switching mechanism directs water through the appropriate measuring section. | Connections with a wide variation between low and peak demand, such as some commercial or institutional services. | Designed to cover a broader flow range than a single meter section. | More complex than a single-element meter. Confirm that the changeover flow and capacity match the demand profile. |
| Electromagnetic (magnetic) | A magnetic field is applied across the flowing water. Electrodes detect a voltage related to flow velocity, which the meter converts to flow rate and volume. | Pipelines where the water is electrically conductive, including many municipal, industrial, and wastewater applications. | No rotor or measuring obstruction in the flow path; can handle water containing suspended solids when properly selected. | Requires conductive liquid, a full pipe for proper measurement, and electrical power. It generally is not suitable for very low-conductivity liquids. |
| Ultrasonic (transit-time) | Ultrasonic signals travel between transducers with and against the flow. The difference in travel time is used to calculate velocity and flow. | Clean-water systems and applications where a non-invasive or low-maintenance flow path is useful; some models clamp onto the outside of a pipe. | No moving parts. Clamp-on models can be installed without cutting the pipe, subject to pipe and measurement conditions. | Performance depends on correct pipe dimensions, sensor placement, flow conditions, and water properties. Bubbles or solids may affect some configurations. |
| Ultrasonic (Doppler) | The meter detects the frequency shift of sound reflected by particles or bubbles moving with the water and uses it to estimate flow velocity. | Certain flows containing enough suspended particles or gas bubbles for a reliable reflected signal. | Can measure some flows where suspended material is present and can be available as a clamp-on design. | Usually unsuitable for clean water without sufficient reflectors. Results depend on particle or bubble concentration and distribution. |