Backflow testing & repair in Redwood City, CA
Redwood City (San Mateo County) gets its water from 2 suppliers, and the one on your water bill sets your backflow rules:
- City of Redwood City Water: you hire a certified tester. We test, file the results with City of Redwood City, and repair failed devices.
- California Water Service – Bear Gulch District: you hire a certified tester. We test, file the results with Cal Water Bear Gulch, and repair failed devices.
- County
- San Mateo County
- Water suppliers
- City of Redwood City Water; California Water Service – Bear Gulch District
- Annual test
- City of Redwood City: owner hires a certified tester and Cal Water Bear Gulch: owner hires a certified tester
- Our price
- $199 per device ($25 off for new customers), or from $180/year on a plan
- ZIP codes
- 94061, 94062, 94063, 94065
City of Redwood City rules for Redwood City customers
- All backflow assemblies (and wells) must be tested or inspected every year.
- Test reports are due within 30 days of the City’s first notice; the customer must ask the City in writing for an extension.
- Routine tests and repairs are reported online through the City’s test entry portal.
- A Redwood City backflow tag must be fixed to each assembly that passes its test.
Source: City of Redwood City backflow program (official page), checked October 19, 2026.
Rules for new and replacement devices in Redwood City
City of Redwood City
- Newly installed assemblies are reported on the City’s paper test form within 15 days.
Source: City of Redwood City backflow program (official page).
Cal Water Bear Gulch
- Only approved, testable backflow prevention assemblies may be installed at the water meter.
- Air gaps must also be inspected every year.
- The assembly installed must be the type Cal Water’s local cross-connection specialist specifies.
Source: Cal Water Bear Gulch backflow program (official page).
Installing or replacing a device takes a licensed plumbing contractor, usually with a permit. We can refer you to one we trust, test the new device once it’s in, and make minor repairs to existing ones.
Backflow questions from Redwood City property owners
Which water supplier serves Redwood City?
Redwood City is split between City of Redwood City Water and California Water Service – Bear Gulch District. Your water bill names your supplier, and its notice sets your backflow rules.
Who tests backflow devices for City of Redwood City customers in Redwood City?
Redwood City accepts backflow test results only from testers on its Qualified Tester List, hired by the customer.
Who tests backflow devices for Cal Water Bear Gulch customers in Redwood City?
Property owners are responsible for their backflow assemblies, which Cal Water requires to be inspected and tested every year by a certified backflow prevention assembly tester.
When is the backflow test due in Redwood City for City of Redwood City customers?
Test reports are due within 30 days of the City’s first notice; the customer must ask the City in writing for an extension.