Technical guide
How entrained air can affect commercial water metering
Air-water flow can influence meter behavior, but not every meter responds the same way and not every high bill is caused by air. Here is what the evidence shows—and how to investigate the issue without jumping to a conclusion.
What “entrained air” means
Entrained air is free gas moving with the water as bubbles, pockets, or a larger air volume. It is different from gas that is fully dissolved in water. When both free air and water cross a meter, the meter is seeing two-phase flow rather than the single-phase water condition for which water meters are normally selected and tested.
Expected operating condition
Response depends on meter and conditions
Why meter technology changes the answer
“Commercial water meter” describes several measurement methods, not one mechanism. The U.S. EPA and AWWA both emphasize choosing the proper meter type and size for the actual consumption pattern and maintaining its accuracy over time.
| Meter family | How it measures | Why free air matters |
|---|---|---|
| Positive displacement | Counts repeated chamber displacement | Air moving the measuring element can register volume under some conditions. |
| Turbine, jet, or compound | Relates rotor speed to flow | Air fraction, pressure, and intermittent pipe filling can change rotor behavior. |
| Ultrasonic | Uses acoustic transit time | Bubbles can disrupt the signal; some meters flag an empty or partially filled pipe. |
| Electromagnetic | Measures conductive liquid velocity | A full pipe and adequate electrode contact are important; free gas reduces the liquid-filled area. |
These are diagnostic considerations, not a prediction for a particular meter. The make, model, size, orientation, installation requirements, and utility test history matter.
What the research does—and does not—establish
A peer-reviewed laboratory study published in Water Resources Management reproduced an intermittent-supply event: an empty service pipe was pressurized and refilled through a mechanical meter. In those test conditions, the meter registered air before the water front arrived, producing over-reading. The researchers also found that air-valve location affected the measured air volume and pressure response.
That is credible evidence for a specific phenomenon, not proof that all commercial meters routinely add the same amount to a bill. The experiment modeled pipe filling after supply interruption. A continuously pressurized building, a different meter technology, or dispersed microbubbles may behave differently. Manufacturer instructions reinforce this variability: for example, Neptune states that retained air can affect its C&I ultrasonic meter’s accuracy, while an empty pipe prevents that model from registering consumption.
Why a commercial water bill may be high
Air is one hypothesis in a broader investigation. Start with the explanations that can be checked directly:
- Billing inputs: confirm the service dates, rate changes, meter multiplier, sewer calculation, and whether the read was actual or estimated.
- Leaks and continuous use: review overnight or closed-hours demand. EPA WaterSense recommends using frequent meter data to identify leaks.
- Operating changes: account for occupancy, irrigation, cooling, laundry, kitchens, cleaning, production, and seasonal demand.
- Meter fit and condition: identify the meter type, size, age, installation orientation, maintenance history, and low-flow performance.
- Air-producing events: document outages, repairs, pressure swings, pump cycling, drained sections, and recurring pipe refill events.
A defensible site investigation
A useful investigation connects the utility bill to physical evidence at the meter. It should be coordinated with the utility, a licensed plumber, or a qualified meter professional; do not modify utility-owned equipment without authorization.
Build the baseline
Collect 12–24 months of bills and available AMI interval data. Separate water volume, sewer charges, rates, and adjustments.
Identify the system
Record meter make, model, size, serial number, pipe size, orientation, pressure range, backflow equipment, pumps, and nearby high points.
Observe conditions
Look for continuous demand, visible leaks, pressure instability, air noise, recent shutdowns, and patterns tied to system refill.
Test the hypothesis
Use an authorized meter accuracy test, calibrated reference meter, or controlled volumetric comparison. Change one condition at a time and document it.
Where Flumera fits
Start with evidence from the property
Flumera’s site assessment reviews utility history, meter and pipe details, access, and operating conditions before recommending a project. The goal is to determine whether a technically suitable, measurable opportunity exists—not to assume every high bill has the same cause.
Request a site assessmentSources and further reading
- U.S. EPA WaterSense at Work: Metering and SubmeteringMeter selection, sizing, installation, data review, and testing guidance for commercial facilities.
- American Water Works Association: Metering and AccountabilityIndustry guidance on proper meter technology, sizing, installation, maintenance, and accuracy testing.
- Water Resources Management: Laboratory investigation of intermittent supplyPeer-reviewed evidence of air-related over-reading during controlled pipe-filling tests; the operating conditions are narrower than normal continuous commercial service.
- Neptune: C&I MACH 10 ultrasonic meter FAQManufacturer-specific documentation that retained air can affect accuracy and an empty pipe can prevent registration.