From The Editor | April 11, 2016

Flow Monitoring, Pressure Management, And Healthy Water Systems

Peter Chawaga - editor

By Peter Chawaga

04_WaterOnline

The Uni-Bell PVC Pipe Association estimates that every day, 850 water main breaks occur in the country. Since the turn of the century, there have been nearly five million such breaks, resulting in over $649 billion in total corrosion costs. The U.S. EPA announced a $271 billion price tag for upgrading and maintaining wastewater infrastructure over the next five years. The AWWA puts the investment needs for buried drinking water infrastructure at more than $1 trillion over the next 25 years.

That’s all to illustrate a well-known truth in the water industry: Pipes are breaking down and putting water and revenue at risk.

Going With The Flow

By flow monitoring, also known as district metering, a utility examines the pattern of water use in a system (usually between 11 p.m. and 5 a.m. when customer demand and flow are low) and can identify potential leaks by watching for elevation.

“Flow monitoring is a concept that has been around but slow to penetrate the U.S. market,” said David Hughes, the water research manager for the Innovation and Environmental Stewardship Department of American Water. “It evolved in Europe, in part because customer metering was lacking, and quantifying leakage was difficult to determine.”

American Water is a utility composed of over 300 distinct systems. It serves 15 million people from California to Ontario. As the nation’s largest publicly traded water utility, it’s as susceptible as any to the perils of the country’s aging infrastructure and the resulting revenue loss. Hughes and other researchers have conducted studies in flow monitoring and have found that the practice reveals crucial, often anomalous, information about a system.

“Through our research on flow monitoring, we have found some unexpected events,” said Hughes. “For example, one system appears to have accurately recorded what we believe was the theft of water from a fire hydrant during consecutive summers, indicated by a sudden, brief increase in flow with a volume that corresponded to the size of a tanker truck.”

Hughes has studied system flow in combination with pressure monitoring and found that the two can provide even more insight into a system when paired together.

“With flow and pressure monitoring, we found an unexpected jump of pressure in a zone caused by a mechanical defect or operator error, followed quickly by evidence of elevated flow,” said Hughes. “The operators were alerted and fixed not one but two leaks. The second leak was detected because the night flow did not return to conditions before the event after the first repair.”

Managing pipe pressure minimizes long-term stress, thus reducing breaks and repairs.

Under Pressure

During last December’s North American Water Loss Conference in Atlanta, Hughes shared his interest in pressure and what it can mean for system leaks in a presentation titled “Leakage Control in Small Systems and Pressure Zones.” His presentation was focused on a practice meant to take place after flow monitoring, once leaks are identified. It’s known as pressure management, effectively reducing pressure in a system with altering pumps or pressure reducing valves (PRVs) to divert water away from defective pipes.

“Flow and pressure in a water-closed system are clearly interrelated,” Hughes said. “Adding flow without water demand to offset it or tanks to store it will increase pressure, and a lack of adequate flow will drop pressure.”

Through pressure management, leak flow can be minimized, and water can be saved. Primarily this is because less water will be streaming toward and out of broken areas of pipe. Secondarily, reducing pressure minimizes the long-term stress on pipes and keeps them intact for longer. Thus, even systems with relatively low leakage can benefit from pressure management.

“Operators need to better understand the merits of pressure management and the potential savings of reduced pressure in portions of their water systems,” said Hughes. “Reducing pressure that still satisfies customer expectations has been shown to reduce leakage and stress on pipe that causes future breaks. This implies that pipe under less pressure will perform longer.”

Hughes invokes a rule of thumb that dictates 1 percent reduction in water loss will result for every 1 psi drop in maximum pressure in a pressure zone.

Still, he is quick to point out that there is no blanket approach to leak detection and prevention that is right for every utility. It’s a notion he sticks to, even while projecting the future of water treatment and how flow monitoring and pressure management will fit within it.

“The industry is already moving toward what is described as the ‘intelligent water system,’” said Hughes. “Flow monitoring and pressure management … are more tools to put in the box. The challenge going forward is to sift through the various approaches and find the best one for each utility operation. But with an aging infrastructure, the push for more efficient operations will drive these techniques to more implementation down the road.”