What is Backflow?

Backflow is a term in plumbing for an unwanted flow of water in the reverse direction. It can be a serious health risk for the contamination of potable water supplies with foul water. In the most obvious case, a toilet flush cistern and its water supply must be isolated from the toilet bowl. For this reason, building codes mandate a series of measures and backflow prevention devices to prevent backflow.

Backflow occurs for one of two reasons, either back pressure or back siphonage.

Back pressure is the result of a higher pressure in the system than in its supply, i.e. the system pressure has been increased by some means. This usually occurs in unvented heating systems, where thermal expansion increases the pressure.

Back siphonage is the result of supply pressure being lowered below that of the system. This occurs when a supply is interrupted or drained down.

How is Backflow prevented?

The simplest method to prevent backflow is to have your backflow assembly tested on an annual basis. For your convenience we provide a list of State Certified Backflow Assembly Testers in our area.

This is not a complete list of all certified testers in this state. Highline Water District (HWD) makes no representation regarding the abilities, performance or quality of service of the testers contained on this list. Further, HWD does not assume or accept any responsibilities for the actions or performance of such testers. This list is provided merely for the convenience of the water service customers who are advised to use their own judgment with respect to contracting with these or any testers.

Contact Us

Highline Water District
23828 30th Ave. S.
Kent, WA 98032
Phone: 206-824-0375
Emergency: 206-824-0375
FAX: 206-824-0806
Hours: M-F 7:00-4:00

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