How To Save Water During Unidirectional Flushing

A common water-industry practice has utilities flushing thousands of gallons of treated water down the drain. But some experts say new technology can make the process more efficient.

Unidirectional flushing is a normal practice for maintaining water lines and ensuring water quality at utilities across the country. The Texas Commission on Environmental Quality, for instance, requires it. A dozen fire hydrants in Dallas were opened for a several days this fall, “spraying 500,000 gallons of water down the drain each day” as the city cleaned its water lines, according to WFAA.

Randall Payton, assistant director at Dallas Water Utilities explained, per the report: “The most important thing you need to know is this is required by state. Personnel strategically close valves to direct water down a single water main creating a velocity that can scour the internal pipe wall. Though these actions may result in brief periods during which customers may observe discoloration in tap water, the water remains safe to drink.”

The downside is that treated water effectively gets flushed down the drain. In Dallas, the recent round of cleaning meant 2.5 million gallons of wasted water, the report said. The utility makes an effort to recollect the water when it can.

“In some areas you’ll notice we hard pipe it and run it back to the sanitary sewer,” Payton said, per the report. “It’s very hard to recollect that water but we do when we can.”

Utility experts agree that recollecting water in the process can be challenging. The city of Livermore, CA, for instance, explains on its website why it does not reuse flushing water.

“Recapturing water discharged through flushing is difficult and not cost-effective. Effectively cleaning the pipes by flushing requires the water to run at high flow rates, which prevents capture. Using water trucks to collect and transport the water is neither cost effective, nor mechanically possible considering the necessary flow velocity and duration to adequately flush the system,” the utility says.

Some utilities are turning to technology to save water during flushing.

“In California, where water conservation is a higher priority, some cities are investing in the Neutral Output Discharge Elimination System or NO-DES trucks which drastically reduces the amount of water sent down the drain,” the report said.

Soquel Creek Water District in California bought the technology for $380,000 and began using it in May during its flushing operations, according to the Capitola Soquel Times. The result was a conservation boost.

“It takes approximately 6 million gallons to flush the District’s distribution system using the traditional method. In addition to saving the 6 million gallons, the NO-DES unit can be used in areas with poor drainage that can’t be flushed properly with the traditional method,” the report said.