What a backflow preventer does
Backflow is water flowing the wrong way in a pipe: the East Bay Municipal Utility District (EBMUD) defines it as “the undesired reversal in the direction of the flow of water”[1]. The City of Round Rock adds that it can cause non-potable water to flow into the public water supply[2].
EBMUD describes a backflow preventer as “a plumbing device that allows water to flow in only one direction, preventing contaminated water from flowing back into the public supply”[1].
Why your utility sent a notice
Some utilities track when each device is due for a test and send the owner a notice. Round Rock sends notifications 30 days before the testing due date[2], and Marin Water mails a notice 45 days before an assembly is due to be tested[4].
How often a test is due differs between utilities. Round Rock says that, depending on the degree of hazard, devices need to be tested either annually or once every 7 years[2]. Marin Water requires annual testing of backflow assemblies[4].
The utility can also decide who may do the test. EBMUD says a test “must be performed by a tester on EBMUD’s Approved Backflow Testers List”[1]. That is why this directory is sorted by utility: each page shows the companies on one utility’s own list, with the list version, the date we fetched it and a link to the original.
A listing is not an endorsement
Marin Water, for example, says it “assumes no liability for the abilities, performance or quality of work performed by individuals listed” and that you should check the tester carries liability insurance[3]. We do not rank, review or recommend companies, and we sort every list A to Z. Confirm with your utility before booking.