By Jake Walsh
With conservation a way of life in California and recent legislation around water loss control and performance standards (Senate Bill 555), every drop of water matters. Understanding the quantities of water delivered to customers and minimizing inaccuracies associated with metering is a critical step for proper water resources management. Fortunately, advances in water metering technologies are allowing utilities to measure water volumes more accurately than ever before.
Mechanical meters are the most common metering technology used today in water distribution systems; however, static meters are becoming a dominant force in the industry. Efforts by American Water Works Association (AWWA) to develop standards around accuracy for static meters have helped these meters gain more widespread acceptance.
Two common types of static meters being evaluated and used by water utilities today are ultrasonic meters and electromagnetic meters, which are battery-powered and use non-mechanical means of measuring water flow. Ultrasonic meters use transducers to send soundwaves through water in the pipe. The time for sound waves to bounce back to the transducers, or transit time, is used to derive the flow rate. Electromagnetic meters use the principle of electromagnetic induction to measure flow. Magnets on the outside of the pipe generate a magnetic field and induce an electrical voltage in the water flowing through, which is measured by electrodes and converted to a flow rate.
With no moving parts, static meters offer some advantages over mechanical meters, including higher metering accuracy over a larger operating range and reduced maintenance requirements.
- Maintained accuracy – Mechanical meters use internal components that rotate or oscillate to measure water flow. The moving parts tend to wear down with use, resulting in these meters generally under-recording water usage over time. With no moving parts, the useful life of static meters is usually determined by battery life rather than accuracy.
- Reduced maintenance – Beyond replacing a static meter when the battery is depleted, static meters do not have moving parts or accessories that require additional maintenance. For example, it is not usually necessary to install strainers that need periodic attention ahead of static meters in potable water applications.
- Larger operating range – Static meters have consistent, high accuracy over their entire operating range, whereas mechanical meters are generally most accurate at medium and high flows. Even mechanical compound meters, which have dual meter chambers to accommodate both low and high flows, have some lost accuracy in the “crossover range” when flow switches between meter chambers. The high accuracy at low flows sets static meters apart and is desirable in California and other areas where regulations now require low-flow water-conserving plumbing fixtures.
- Low flow detection – All water meters have a lower limit of flow that can be accurately registered. For static meters, this limit is lower, which allows static meters to pick up ultra-low flows that would otherwise be missed, resulting in reduced apparent losses and lost revenue for the utility. When coupled with Advanced Metering Infrastructure (AMI) and the ability to send near real-time data over a remote communications network, static meters become an even more powerful tool for water loss control. Not only can smaller leaks be measured by static meters, but the utility and customer can be promptly notified of the leak with AMI. Even small leaks can contribute to significant water loss over time if left undetected.
AMI programs often provide utilities with an opportunity to pivot from traditional metering technologies to static meters. In 2022, the California Public Utilities Commission approved AMI across the entire San Jose Water distribution system, which consists of about 230,000 meters. San Jose Water is actively evaluating various static meters. The selection process is based on meter technology, availability, the ability of the meter to communicate necessary information through the selected AMI network, and cost.
There is a higher upfront capital cost associated with static meters, and ultimately, the most suitable metering technology will be utility specific. In California, where we experience frequent, recurring and extreme droughts, every drop of water counts, and the potential benefits of revenue recovery and water loss control warrant an evaluation of static meters. By understanding all our options for metering technologies, we can make more informed decisions in managing our water resources.
Jake Walsh is assistant chief engineer of planning at San Jose Water. He has 18 years of experience in public water utility engineering at San Jose Water, serving over 1 million people in the greater San Jose metropolitan area. He earned his Master of Public Administration degree from the University of San Francisco.
