Friday, May 7, 2021
May 7, 2021

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Energy Advisor: Backflow is rare but must be prevented


When you turn on the tap, you’re probably not thinking about the massive network of pipes connecting your home to everyone else in the community or the legion of pumps that harness the tremendous kinetic energy required to pull our water from deep underground and drop it into your hands at a comfortable and convenient pressure. And you probably don’t think about what would happen if the water suddenly started flowing in reverse, or the dangers it could pose to our water supply.

The Clark Public Utilities Water Utility, along with other water utilities in our region, makes huge investments to ensure that doesn’t happen. But the possibility is there, and that’s why backflow-prevention devices are so important.

Backflow is a plumbing term for water flowing in reverse of its intended direction. So rather than the water being pushed out of a pipe, it’s drawn back in. When that happens, it can create a vacuum that could pull harmful substances into a home’s, neighborhood’s or entire community’s drinking supply.

Fortunately, backflow is a rare phenomenon. It usually happens only if there’s a significant event in the water system, like a main break, or if a large amount of water is used in firefighting near your connection. But when it does happen, harmful lawn and garden chemicals or other unwanted liquids can get into the water supply.

“That’s why backflow-prevention devices are so important,” said Gary St John, water-quality specialist at Clark Public Utilities. “Properties with irrigation systems, automatic lawn sprinklers or large dedicated fire-suppression systems should have their backflow preventers inspected and tested at least once a year.”

Unless they have an in-ground irrigation system, backflow isn’t an issue most people have to worry about. Homes and buildings are plumbed with fixtures that have air gaps in place to stop backflow from happening. Even many lawn and garden sprinkler systems were built with devices called atmospheric vacuum breakers, or AVBs for short. Like the fixtures in the home, these create an air gap at the system’s water connection.

The one place a homeowner might run into backflow is at the garden hose. Since the 1990s, homes have been built with vacuum breaker-equipped hose spigots, but many older homes don’t have them. To prevent possible backflow, replace old spigots with ones that are vacuum breaker-equipped, or remember to never leave a hose submerged after it’s been shut off.

St John said it’s common for people to have a backflow-prevention device at their property and not realize it.

“I’ve had multiple conversations with customers who are new to our area — people who just bought the house, and this is the first they’ve ever heard of backflow prevention or backflow testing,” he said.

To see if you have a backflow preventer on your irrigation system, look for an in-ground rectangle box with a green cover — they’re by the water meter or perimeter of the house. If you have a backflow assembly, it’ll be in there.

Backflow-prevention assembly testing is required by law. The Clark Public Utilities Water Utility urges its customers to have their backflow-prevention devices tested in the spring, just before their irrigation season begins. Testing doesn’t take long and doesn’t cost much.

The utility even keeps a list of backflow testers in our area that customers can access. Tester participation on our list is voluntary and not a recommendation or warranty of any kind — but it is a helpful place to start.

Customers can also join the utility’s automatic backflow testing program to have their devices tested by a local, certified backflow assembly tester who is hired by the utility through a bidding process. Just call the utility’s dedicated backflow line at 360-992-8589.

If you’re a Clark Public Utilities water customer and you’re not sure if you have a backflow assembly, call 360-992-3000. An employee will search for your address in the records; if it’s not there, the employee can send a service technician out to inspect the site.

“We can only check our water service customers, who are typically in the unincorporated parts of the county,” St John said. “Customers serviced by another municipality should call them to find out next steps.”

Energy Adviser is written by Clark Public Utilities. Send questions to or to Energy Adviser, c/o Clark Public Utilities, P.O. Box 8900, Vancouver, WA 98688.