What backflow is
Water normally flows one way, from the street main into the building. If pressure in the main drops, for example during a main break or heavy firefighting, water can be pulled backward. Without protection, water from an irrigation line, a boiler, a fire sprinkler system or a process connection could be drawn back into the public supply.
A backflow prevention assembly sits on the supply line and allows water through in one direction only. Water providers in California have cross-connection control programs, and many require certain properties to install assemblies and have them tested on a schedule. Your water provider sets the specific requirement for your connection.
Backflow terms
- Cross-connection
- Any point where drinking water piping could connect to a non-drinking source.
- Back-siphonage
- Backflow caused by a drop in supply pressure that pulls water backward.
- Back-pressure
- Backflow caused by pressure on the property side exceeding supply pressure.
- RP assembly
- A reduced pressure principle assembly, used for higher-hazard connections, with a relief valve that discharges water if it detects a problem.
- Double check valve assembly
- Two check valves in series, used for lower-hazard connections such as many fire sprinkler systems.
- Certified tester
- A person certified to test backflow assemblies and submit results to the water provider.
Properties that commonly have backflow assemblies
- Restaurants, salons, medical and dental offices.
- Shopping centers, office buildings and industrial units.
- Properties with dedicated irrigation meters.
- Buildings with fire sprinkler systems.
- Multi-unit residential properties, depending on the connection.
- Homes with pools, boilers or other connections the provider identifies.
How annual testing usually works
- Notice from the provider.Many water providers send a notice when a test is due. Keep it, since it lists the assembly and the deadline.
- Schedule a certified tester.Ask for proof of current certification and, for repairs, a CSLB-licensed contractor.
- Test the assembly.The tester measures valve performance with a test kit while water is briefly shut off.
- Repair if needed.Failed assemblies usually need new springs, seals or checks, then a retest.
- Submit results.Results go to the water provider. Keep a copy for your records.
Commercial plumbing needs that differ from homes
| Need | Why it matters for a business |
|---|---|
| Grease interceptors | Food service drains need grease controls; maintenance rules come from the city or sewer agency. |
| Scheduled after-hours work | Repairs often have to happen outside business hours to avoid closing. |
| Larger water heaters and boilers | Commercial equipment has its own venting, relief and inspection requirements. |
| Multiple tenants on shared lines | A clog or shutoff affects more than one business, so communication matters. |
| Accessibility fixtures | Restrooms may need fixtures meeting accessibility rules during remodels. |
Questions for a commercial plumbing contractor
- Is your CSLB license active, and do you carry the insurance my lease or landlord requires?
- Are your backflow testers certified, and will you submit results to the water provider?
- Can you schedule work after hours?
- Will you provide a written scope and any permit paperwork?
Common questions
Does a single-family home need backflow testing?
Most homes do not have a testable assembly unless they have a dedicated irrigation meter, a fire sprinkler system or another connection the provider flags. Check with your water provider.
What happens if a backflow test is missed?
Water providers set their own enforcement steps, which can include follow-up notices and, in some cases, service interruption. Check with your provider.
My RP assembly is dripping from the relief valve. Is it broken?
Discharge from the relief valve means the assembly detected a pressure condition or a part is worn. Have a certified tester or plumber check it.
General information for La Mirada, not a quote or professional advice. In an emergency, call 911.