Flushing Dead-End Water Pipes

Water Systems Lead Operator Danny Leonardo opens the hydrant used to flush a drinking water main at the end of Trescott Court.

Field Operators routinely flush drinking water lines to maintain water quality as it moves through the 321 miles of potable water pipes in DSRSD’s service area. Flushing water pipes is particularly important on the District’s 747 dead-ends, such as pipes that end on a cul-de-sac.

“Over the course of time, there is a natural buildup of biological material in the water main,” says Water/Wastewater Systems Superintendent Dan Martin. “Water is full of normal organisms, nonpathogens. By using a chlorine disinfectant, we keep these normal organisms from creating an environment where unhealthy organisms, or pathogens, can grow. The naturally occurring organisms will accumulate over time, and we want to keep the population at a normal level by flushing on a routine basis as preventative measure.”

Flushing water lines involves scouring the walls of pipes with pressurized water. Since July, 2019, the District has been replacing 2-inch blow-off valves, located at dead-ends, with 4-inch blow-off valves. A larger blow-off valve allows operators to increase flushing velocity from 250 gallons per minute up to 900 gallons per minute. “This increase in the speed of water flowing through the pipes improves cleaning,” Martin says.

Senior Water/Wastewater Systems Operator Matt McGrath checks the turbidity of water after flushing.

Operators return the flushed water into the sewer system so it can be treated at the Regional Wastewater Treatment Facility and converted into recycled water for irrigation. This is especially helpful during a drought when the summer months are hot and dry.

DSRSD’s goal is to flush all dead-ends annually during summer and fall. Operations staff are getting closer to that goal, currently flushing all dead-ends about every year and a half, with no location going longer than two years. The District is also designing water distribution systems differently so there are  fewer dead-ends added to the system. Instead, they loop pipes.

System maintenance included with flushing

While performing flushing, crews also exercise fire hydrant and isolation valves to ensure they are in good operating condition. As of summer 2021, there were 12,697 valves. Operators have a goal of exercising valves every four years, and are currently at every five years—increasing the number each year. In 2020, the District exercised 2,343 valves.

“Most valves are in the open position, but periodically we may have to shut a valve to isolate a leak,” Martin says. “The valves can degrade when not being used, and sometimes when staff go to operate valves, they won’t move, will break, or can’t seal fully. You have to exercise them on a reasonable interval.”

Updated: July 14, 2021