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Got a CPC 603.2 correction?

Backflow prevention

For builders in California, Greater Seattle, the Las Vegas area, the Denver area and Kansas City · CrossBeam Permits

What this code requires, how to fix it, and how cities and counties review it

What this code requires

CPC 603.2 requires every backflow prevention device or assembly to be approved by the Authority Having Jurisdiction and to comply with Table 603.2, which matches the device to the degree of hazard (pollution or contamination) and to whether the connection sees backsiphonage or backpressure. Specific uses in CPC 603.5 narrow the choice. Irrigation with no pumps or chemical injection takes an AVB, PVB, SVB, or RP; add a chemical injector and an RP is required. Boiler makeup water takes a double check, a vented preventer with pressure reducing valve, or an RP, and an RP where chemicals are added. Assemblies are tested at installation and at least annually.

How to fix it

  1. Identify every cross-connection on the plumbing plans

    Walk each plumbing system on your drawings and flag every point where the potable supply connects — or could connect — to equipment, a non-potable source, or a system that uses chemical additives. Common locations: irrigation laterals at the meter, boiler or hydronic makeup water lines, fire sprinkler system tie-ins, pools and spas, solar thermal systems, hose bibbs at commercial sinks, and any equipment with a direct water connection. List each connection and its use before picking a device.

  2. Classify the hazard degree for each connection

    CPC Table 603.2 ties device selection to hazard degree. High hazard means the backflow could introduce substances that are toxic, poisonous, or otherwise health-threatening — irrigation with fertilizer or pesticide injection, boiler systems with chemical treatment, and fire sprinkler systems that may contain glycol or biocides all qualify. Low hazard means contamination would be objectionable but not health-threatening — most clean commercial process water connections without chemical additives fall here. When in doubt, the local water purveyor's cross-connection control program has a hazard classification table; call them before the design is finalized.

  3. Select the correct device type for each hazard level

    Use this as your baseline: RPZ (reduced pressure principle) assemblies cover high-hazard connections under backpressure or backsiphonage. Double check valve assemblies (DCVA) cover low-hazard connections only, and a pit or vault install needs prior AHJ approval. Atmospheric vacuum breakers (AVB) handle backsiphonage only, at least 6 inches above downstream piping, and can't be under pressure more than 12 hours in 24. Pressure vacuum breakers (PVB) are common for irrigation but must sit at least 12 inches above all downstream piping. For irrigation, CPC 603.5.6 allows only an AVB, PVB, SVB, RP, or IAPMO PS 72 valve, and an RP where chemicals are injected; a DCVA is not on that list. Confirm the device type with both the CPC table and your water purveyor — some cities have stricter requirements than the state code minimum.

  4. Show every device on the plumbing plan sheets

    The plan-checker needs to see each backflow prevention assembly drawn in at its actual location. Use the device abbreviation (RPZ, DCVA, PVB, AVB) as a callout tag and add a note that states: device type, manufacturer series if specified, and installation orientation. For IRR (irrigation) connections, show the assembly between the meter and the first distribution point. For boiler makeup lines, show the assembly on the cold water feed before it enters the boiler room. Don't put this in a general notes block only — it needs to appear graphically on the relevant sheet.

  5. Add a detail or riser diagram for RPZ assemblies

    RPZ assemblies require more plan detail than simpler devices. Show a riser diagram or plan detail at a readable scale that includes: the shutoff valves on each side, the test cocks, the required clearances for testing access (not less than 12 inches of clearance at the bottom, plus the manufacturer's access clearances), the relief valve discharge point and its air gap termination, and the drain or flood containment if the assembly is indoors. Plan-checkers check this detail specifically because an improperly located RPZ that can't be tested is as good as no protection at all.

  6. Verify water purveyor approval requirements

    Southern California's water purveyors — including Anaheim Public Utilities and other OC distributors — require cross-connection control surveys and device approvals that run parallel to the building permit. Call your local water utility before submitting plans and confirm: (1) which device types they accept on their approved product list, (2) whether they require a separate cross-connection control permit, and (3) testing requirements after installation. Getting a building permit approved but failing the utility's separate inspection is a real outcome — address both at the same time.

  7. Coordinate with the fire sprinkler designer

    If the project includes a fire sprinkler system, the backflow preventer at the domestic/fire tie-in is often in a gray zone between the plumbing contractor and the fire sprinkler designer. Confirm in writing which contractor is providing the assembly, who shows it on which set of plans, and who pulls the permit for it. Backflow assemblies on fire sprinkler connections are also governed by the NFPA 13, 13R, or 13D sprinkler standard and the local fire authority, so the assembly may need to appear on both the plumbing plans and the fire sprinkler submittals. Missing from either set will trigger a correction.

  8. Schedule field testing before final inspection

    CPC 603.4.2 requires every backflow prevention assembly to be tested by a certified backflow assembly tester at installation and at least annually after that. The tester fills out the water purveyor's test report form, and that report goes to the purveyor. Some jurisdictions also require the test report before they sign off on the plumbing final inspection. Book your tester early — in busy periods, a two-week lead time is common. Don't wait until the day before final.

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Why you got flagged

Plan-checkers flag CPC 603.2 most often when backflow prevention devices simply don't appear on the plumbing plans at all. Irrigation systems are the most common miss — a contractor shows the lateral, the meter, and the distribution heads, but skips the backflow assembly at the service connection. Without it on the drawings, the plan-checker has no way to confirm the correct device type was selected, and the sheet comes back.

The second scenario is device type mismatch. A double check valve assembly is shown on a boiler makeup water line that feeds a chemical treatment system. That's a high-hazard cross-connection, and a double check valve doesn't cut it — an RPZ is required. CPC 603.5.10 requires an RP wherever chemicals are introduced into a boiler system, and the plan-checker will flag the discrepancy even if a device is drawn in.

Fire sprinkler tie-ins are a third common trigger. Residential fire sprinkler systems pull from the domestic water supply, and the water purveyor or fire authority may require a backflow preventer at that connection. Contractors who handle the plumbing permit separately from the fire sprinkler permit sometimes leave the backflow device off both sets of plans, each assuming the other trade covered it. Neither set passes.

A fourth scenario shows up on tenant improvement work: an existing plumbing system gets a new process connection (lab sink, chemical dispenser, janitorial mop sink with a hose bibb) without the plans calling out the required vacuum breaker or other protection device. The plan-checker spots the new connection and pulls the drawings for the backflow note that isn't there.

The official code

2025 California Plumbing Code Section 603.0 — Cross-Connection Control

Read the source →

Common questions

Do I need an RPZ or a double check valve for my irrigation system?
It depends on whether the system has pumps or chemical injection. Under CPC 603.5.6, an irrigation system with no pumps and no chemical injection can be protected by an atmospheric vacuum breaker (AVB), a pressure vacuum breaker (PVB), a spill-resistant vacuum breaker (SVB), an RP, or a valve complying with IAPMO PS 72. A double check valve assembly is not one of the listed options. If the system has a pump or anything else that can create backpressure, an RP is required where the device sits upstream of that source. The moment you add a fertigation system, injector, or any chemical treatment, an RP is required. Your water purveyor may add its own rules, so check with them before the design is final.
Where does the backflow assembly go relative to the water meter?
The assembly goes on the customer's side of the meter, between the meter and the first branch to the protected equipment. For irrigation, it's installed on the dedicated irrigation lateral before the first head or valve. The device needs to be accessible for annual testing — don't bury it in a non-accessible vault or hide it behind equipment. CPC 603.4.3 requires the manufacturer's access clearances and not less than 12 inches between the lowest part of the assembly and the grade, floor, or platform, plus a platform if the assembly sits more than 5 feet up.
Does a residential hose bibb need a backflow preventer?
In most cases, yes. CPC 603.5.7 requires potable water outlets with hose attachments, other than water heater drains, boiler drains, and clothes washer connections, to be protected by a nonremovable hose bibb-type backflow preventer, a nonremovable hose bibb-type vacuum breaker, or an atmospheric vacuum breaker at least 6 inches above the highest point of usage. They're not field-tested the same way an RPZ is, but they do need to be shown on the plans for new construction and shown as part of any plumbing scope that includes new hose bibbs. Plan-checkers flag missing vacuum breaker callouts on hose bibbs regularly, especially on ADU projects and accessory structures.
Who certifies backflow assembly testers in California?
The CPC requires testing and maintenance by a certified backflow assembly tester or repairer, certified under ASSE/IAPMO/ANSI Series 5000 or another certification approved by the Authority Having Jurisdiction. Each water purveyor can also keep its own approved tester list, so ask yours for it before you hire. The test must happen at installation and at least annually after that (CPC 603.4.2), and the completed report goes to the utility.
Can a backflow preventer be installed indoors?
Yes, with conditions. An RP assembly can discharge water through its relief valve, so an indoor install needs a drain line sized for the manufacturer's discharge rate (CPC 603.4.8), and potable water discharged to the drainage system must pass through an approved air gap. The manufacturer's access clearances and at least 12 inches under the lowest part of the assembly still apply (CPC 603.4.3). Devices with atmospheric vents or ports cannot go in pits, underground, or where there are toxic or corrosive fumes (CPC 603.4.9). Double check valve assemblies do not discharge water but still need test cock access. Confirm with your water purveyor, since some require outdoor installation for inspection access.
Is a backflow preventer required on a fire sprinkler system in a single-family home?
It depends on the system and the local authorities rather than a blanket CPC rule. CPC 612.1 sends residential sprinkler systems to the California Residential Code or Fire Code, and the CPC fire-system backflow section (603.5.14) carries a California note that it is not adopted by the State Fire Marshal. That note quotes Health and Safety Code 13114.7, under which class 1 and class 2 sprinkler systems (no antifreeze or additives) need no backflow equipment at the service connection beyond what the NFPA sprinkler standard requires. If the system uses antifreeze or other chemicals, expect an RP. Get the water purveyor's and fire authority's requirement in writing, and show the device, or why none is needed, on both the plumbing plans and the fire sprinkler submittals.

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