CPC · California Plumbing Code

What are the supply fitting and backflow prevention requirements at fixtures?

Every plumbing fixture’s supply fittings must be installed to prevent backflow under the CPC (see § 402.7), and the fixture’s mounting or fitting must not defeat or obstruct that backflow protection (see § 402.9). Follow the Chapter 6 device selection and the manufacturer’s installation instructions.

Ask a question free See coverage

Last reviewed: July 6, 2026

What the code requires — 2-4 sentences

The supply lines and fittings for every plumbing fixture must be installed so they prevent backflow in accordance with the cross‑connection and backflow control provisions in Chapter 6 — this is the baseline rule in § 402.7. In addition, fixtures must be installed per the manufacturer’s instructions and the means of backflow prevention must not be compromised by the fixture fitting mounting surface — this is required by § 402.9.

The single most important rule: supply fittings at every fixture must be installed to prevent any backflow (follow Chapter 6), and you cannot mount or install a fitting in a way that defeats the backflow protection.

Requirements in detail

Short rule (what to do)

  • Install every fixture’s supply piping and fittings so they prevent backflow in accordance with Chapter 6 (cross‑connection control). § 402.7.
  • Install the fixture per the manufacturer’s instructions and ensure the mounting surface or fitting installation does not compromise the backflow prevention. § 402.9.

What “in accordance with Chapter 6” means (where Chapter 6 provides details)

Chapter 6 (Chapter 603 and related tables/sections) spells out:

  • Approved devices and methods (air gap, AVB, PVB, RP, dual check, etc.) and when each applies (see Table 603.2 and Section 603.3).
  • Specific fixture requirements (for example, atmospheric vacuum breakers on certain flushometer valves and vacuum‑breaker requirements for urinals and other fixtures) and rules for listing, installation, freeze protection, and prohibited locations.

Decision table — when and what to install (decision-relevant dimensions)

Decision question Required action / threshold Typical device options Code Reference
Does the fixture supply need protection? Yes — every plumbing fixture’s supply lines/fittings must prevent backflow Use the backflow device/method required by Chapter 6 (air gap, AVB, PVB, RP, etc.) § 402.7
Can a fixture’s mounting or fitting defeat backflow protection? No — mounting surface or fitting installation must not compromise backflow prevention Adjust mounting or use listed integral backflow fittings; follow manufacturer instructions § 402.9
If a faucet has a pull‑out hose or a handheld shower Use fittings with integral backflow protection or add an approved backflow device that meets the referenced ASME/ASSE standard ASME A112.18.1 (integral) or ASME A112.18.3 (backflow device) per fixture type ASME/fixture rules referenced in CPC (see ASME citations)
Where Chapter 6 prescribes a specific device for a fixture Follow the specific device / critical‑level / installation rule in Chapter 6 (e.g., AVB critical levels for flushometers) See Section 603.5 specifics (e.g., 603.5.1, 603.5.2) Chapter 6 (603.x)

(Use the table as a quick decision aid — always confirm the exact device/type in Chapter 6 and any fixture‑specific CPC paragraphs or referenced standard.)

Installation notes / practical points (all grounded to the code)

  • Follow the manufacturer’s installation instructions for the fixture and any integral backflow device — CPC requires compliance with manufacturer instructions. § 402.9.
  • If a fixture contains an integral backflow preventer or integral air gap manufactured as a unit, that unit must be installed in accordance with its listing and manufacturer instructions (Chapter 603 referencing integral assemblies).
  • Chapter 6 also controls device siting, freeze protection, prohibited locations (vents/ports not in pits), maintenance and testing requirements — the CPC delegates device selection/installation detail to Chapter 6.

Exceptions & special cases

  • Integral units: If a fixture or fitting is listed with an integral backflow device or an integral air gap, install per the listing/manufacturer — that may substitute for a separate device (see Chapter 603, integral device language).
  • Fixture‑specific rules: Some fixtures have their own backflow language (for example, urinals and flushometer valves have vacuum‑breaker or critical‑level requirements) — follow the specific 603.5 subsections for those fixtures.
  • Location limits: Devices with atmospheric vents/ports may not be installed in pits, underground, or submerged locations; do not place vented devices where toxic/corrosive fumes exist. (Chapter 603 general requirements.)

If a needed detail for a particular fixture type is not found in § 402.7 or § 402.9, consult Chapter 6 (603.x) and the CPC fixture sections (e.g., the urinal or faucet sections) and the referenced ASME/ASSE standards cited by those sections. The CPC text retrieved here shows these cross‑references; consult those paragraphs for device selection and critical dimensions.

Common mistakes

  • Installing a supply fitting without any backflow protection because “it’s just a sink” — § 402.7 requires protection for every fixture’s supply lines/fittings.
  • Mounting or trimming a fixture so an integral backflow device is obstructed or rendered inoperative — § 402.9 forbids compromising the means of backflow prevention.
  • Assuming a dual check or generic check valve is acceptable for all hazards— Chapter 6 (Table 603.2 and 603.5) specifies the device type by hazard/fixture. Check the Chapter 6 table before selecting a device.
  • Installing a vented device (e.g., RP assembly with vents) in a pit or submerged location — Chapter 603 prohibits atmospheric vents/ports in such locations.

Worked example — lavatory with pull‑out faucet (concrete scenario)

Scenario: New lavatory in a commercial restroom will be fitted with a pull‑out spray faucet. The faucet manufacturer offers two options: (A) faucet with an integral backflow device listed to ASME A112.18.1 (integral), or (B) standard faucet plus an external backflow device listed to ASME A112.18.3.

Application of the code:

  1. Baseline: Every fixture supply fitting must prevent backflow — § 402.7. So the lavatory cannot be left unprotected.
  2. Mounting/installation: The faucet must be installed so the backflow protection is not compromised (e.g., do not cap access to an integral device) — § 402.9.
  3. Device selection: The CPC allows either an integral listed backflow means or a separate listed backflow device that meets the referenced ASME/ASSE requirements for that fixture type (ASME A112.18.1 for plumbing supply fittings with integral protection or ASME A112.18.3 for backflow protection devices in fixture fittings). So either option (A) or (B) is acceptable provided the unit used is listed and installed per its listing/manufacturer.

Numeric example (not a pressure calculation — sizing not required here): choose option (A). Install the listed integral device per the manufacturer and ensure the faucet mounting does not block the device or its critical components. Inspectors will verify: (1) that backflow protection exists and (2) that installation did not defeat the device. If option (B) is chosen, install the separate listed device upstream as required by its listing and Chapter 6 guidance.

Related provisions

  • § 402.7 — Supply fittings: supply lines/fittings must prevent backflow (primary requirement).
  • § 402.9 — Fixture installation and not compromising backflow prevention (mounting surface requirement).
  • § 603.0 / Chapter 6 — Cross‑connection control, device approvals, and general backflow prevention layout and rules.
  • § 603.3 — Types of backflow prevention devices and definitions (air gap, AVB, PVB, RP, etc.).
  • § 603.5 — Specific requirements for certain fixtures and installations (for example, AVB critical level rules, ballcock requirements, fixture‑specific protection).
  • Fixture sections that reference backflow protection (examples): § 412.2 (urinals — vacuum breaker requirement) and sections on faucets/handheld showers that reference ASME/ASSE standards.

(When selecting the exact device and installation method for a given fixture, always consult the Chapter 6 tables/paragraphs and the referenced ASME/ASSE standards identified in those CPC paragraphs.)

Code references

Grounded in the retrieved California Plumbing Code — click a citation to read the verbatim passage:

  • CPC § 402.6.2 High relevance — show source text

    Closet rings (closet flanges) shall be adequately designed and secured to support fixtures connected thereto.

    402.6.2 Securing Closet Flanges. Closet screws, bolts, washers, and similar fasteners shall be of copper alloy, copper, or other listed equally corrosion-resistant materials. Screws and bolts shall be of a size and number to properly support the fixture installed. 402.6.3 Securing Floor-Mounted, Back-Outlet Water Closet Bowls. Floor-mounted, back-outlet water closet bowls shall be set level with an angle of 90 degrees (1.57 rad) between the floor and wall at the centerline of the fixture outlet. The floor and wall shall have a flat mounting surface not less than 5 inches (127 mm) to the right and left of the fixture outlet centerline. The closet flange shall be secured to the wall mounting surface. Offset, eccentric, or reducing closet flanges shall not be permitted with these fixtures.

    The fixture shall be secured to the wall outlet flange or drainage connection and the floor by corrosion-resistant screws or bolts.

    402.7 Supply Fittings. The supply lines and fittings for every plumbing fixture shall be so installed as to prevent backflow in accordance with Chapter 6.

    402.8 Installation. Fixtures shall be installed in accordance

    with the manufacturer’s installation instructions.

    402.9 Design and Installation of Plumbing Fixtures. Plumbing fixtures shall be installed in accordance with the manufacturer’s installation instructions. The means of backflow prevention shall not be compromised by the designated fixture fitting mounting surface. 402.10 Slip Joint Connections. Fixtures having concealed slip joint connections shall be provided with an access panel or utility space not less than 12 inches (305 mm) in its least dimension and so arranged without obstructions as to make such connections accessible for inspection and repair. 402.11 Future Fixtures. Where provisions are made for the future installation of fixtures, those provided for shall be considered in determining the required sizes of the drain and water supply piping. Construction for future installations shall be terminated with a plugged fitting or fittings. Where the plugged

    fitting is at the point where the trap of a fixture is installed, the plumbing system for such fixture shall be complete and be in accordance with the plumbing requirements of this code.

    403.0 Accessible Plumbing Facilities. 403.1 General. Where accessible facilities are required in applicable building regulations, the facilities shall be installed in accordance with those regulations. [HCD 1-AC] For spe- cific requirements regarding accommodations for persons with disabilities, see Chapter 11A of the California Building Code. 403.2 Fixtures and Fixture Fittings for Persons with Disabilities. Plumbing fixtures and fixture fittings for persons with disabilities shall be in accordance with ICC A117.1 and the applicable standards referenced in Chapter 4. [HCD 1-AC] Specific requirements regarding accommodations for persons with disabilities are contained in Chapter 11A of the California Building Code. 403.3 Exposed Pipes and Surfaces. Water supply and drainpipes under accessible lavatories and sinks shall be insulated or otherwise be configured to protect against contact. Protectors, insulators, or both shall comply with ASME A112.18.9 or ASTM C1822.

  • CPC § 402.6.1 High relevance — show source text

    Wall-mounted water closet fixtures shall be securely bolted to an approved carrier fitting. The approved carrier fitting shall be securely attached to the structure. The connecting pipe between the carrier fitting and the fixture shall be an approved material and designed to accommodate an adequately sized gasket. Gasket material shall be neoprene, felt, or similar approved types.

    402.6.1 Closet Rings (Closet Flanges). Closet rings (closet flanges) for water closets or similar fixtures shall be of an approved type and shall be copper alloy, copper, hard lead, cast-iron, galvanized malleable iron,

    2025 CALIFORNIA PLUMBING CODE 59

    ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

    PLUMBING FIXTURES AND FIXTURE FITTINGS

    ABS, PVC, or other approved materials. Closet rings (closet flanges) shall be approximately 7 inches (178 mm) in diameter and, where installed, shall, together with the soil pipe, present a 1 [1] ⁄ 2 inch (38 mm) wide flange or face to receive the fixture gasket or closet seal.

    Caulked-on closet rings (closet flanges) shall be not less than [1] ⁄ 4 of an inch (6.4 mm) thick and not less than 2 inches (51 mm) in overall depth.

    Closet rings (closet flanges) shall be burned or soldered to lead bends or stubs, shall be caulked to cast-iron soil pipe, shall be solvent cemented to ABS and PVC, and shall be screwed or fastened in an approved manner to other materials.

    Closet bends or stubs shall be cut-off to present a smooth surface even with the top of the closet ring before the rough inspection is called.

    Closet rings (closet flanges) shall be adequately designed and secured to support fixtures connected thereto.

    402.6.2 Securing Closet Flanges. Closet screws, bolts, washers, and similar fasteners shall be of copper alloy, copper, or other listed equally corrosion-resistant materials. Screws and bolts shall be of a size and number to properly support the fixture installed. 402.6.3 Securing Floor-Mounted, Back-Outlet Water Closet Bowls. Floor-mounted, back-outlet water closet bowls shall be set level with an angle of 90 degrees (1.57 rad) between the floor and wall at the centerline of the fixture outlet. The floor and wall shall have a flat mounting surface not less than 5 inches (127 mm) to the right and left of the fixture outlet centerline. The closet flange shall be secured to the wall mounting surface. Offset, eccentric, or reducing closet flanges shall not be permitted with these fixtures.

    The fixture shall be secured to the wall outlet flange or drainage connection and the floor by corrosion-resistant screws or bolts.

    402.7 Supply Fittings. The supply lines and fittings for every plumbing fixture shall be so installed as to prevent backflow in accordance with Chapter 6.

    402.8 Installation. Fixtures shall be installed in accordance

    with the manufacturer’s installation instructions.

    402.9 Design and Installation of Plumbing Fixtures. Plumbing fixtures shall be installed in accordance with the manufacturer’s installation instructions. The means of backflow prevention shall not be compromised by the designated fixture fitting mounting surface. **402.10 Slip Joint Connections.

  • CPC § 603.4.5 High relevance — show source text

    603.4.5 Hot Water Backflow Preventers. Backflow preventers for hot water exceeding 110°F (43°C) shall be a type designed to operate at temperatures exceeding 110°F (43°C) without rendering a portion of the assembly inoperative. 603.4.6 Integral Backflow Preventers. Fixtures, appliances, or appurtenances with integral backflow preventers or integral air gaps manufactured as a unit shall be installed in accordance with their listing requirements and the manufacturer’s installation instructions.

    603.4.7 Freeze Protection. In cold climate areas, backflow assemblies and devices shall be protected from freezing with an outdoor enclosure that complies with ASSE 1060 or by a method acceptable to the Authority Having Jurisdiction. 603.4.8 Drain Lines. Drain lines serving backflow devices or assemblies shall be sized in accordance with the discharge rates of the manufacturer’s flow charts of such devices or assemblies.

    603.4.9 Prohibited Locations. Backflow prevention devices with atmospheric vents or ports shall not be installed in pits, underground, or submerged locations. Backflow preventers shall not be located in an area containing fumes that are toxic, poisonous, or corrosive. 603.5 Specific Requirements. Specific requirements for backflow prevention shall comply with Section 603.5.1 through Section 603.5.22. 603.5.1 Atmospheric Vacuum Breaker. Water closet and urinal flushometer valves shall be protected against backflow by an approved backflow prevention assembly, device, or method. Where the valves are equipped with an atmospheric vacuum breaker, the vacuum breaker shall be installed on the discharge side of the flushometer valve with the critical level not less than 6 inches (152 mm), or the distance according to its listing, above the overflow rim of a water closet bowl or the highest part of a urinal.

    603.5.2 Ballcock. Water closet and urinal tanks shall be equipped with a ballcock. The ballcock shall be installed with the critical level not less than 1 inch (25.4 mm) above the full opening of the overflow pipe. In cases where the ballcock has no hush tube, the bottom of the water supply inlet shall be installed 1 inch (25.4 mm) above the full opening of the overflow pipe.

    603.5.3 Backflow Prevention. Water closet flushometer tanks shall be protected against backflow by an approved backflow prevention assembly, device, or method.

    603.5.4 Heat Exchangers. Heat exchangers used for heat transfer, heat recovery, or solar heating shall protect the potable water system from being contaminated by the

    heat-transfer medium. Single-wall heat exchangers used in indirect-fired water heaters shall meet the requirements of Section 505.4.1. Double-wall heat exchangers shall separate the potable water from the heat-transfer medium by providing a space between the two walls that are vented to the atmosphere. 603.5.5 Water Supply Inlets. Water supply inlets to tanks, vats, sumps, swimming pools, and other receptors shall be protected by one of the following means:

    (1) An approved air gap.

    (2) A listed vacuum breaker installed on the discharge side of the last valve with the critical level not less than 6 inches (152 mm) or in accordance with its listing.

  • CPC § 0.76 High relevance — show source text

    [BSC-CG & DSA-SS] Metering faucets for wash foun- tains shall have a maximum flow rate of not more than 0.20 gallons (0.76 L) per cycle/20 [rim space (inches) at 60 psi] in compliance with Chapter 5, Division 5.3 of the California Green Building Standards Code (CALGreen).

    417.2 Deck Mounted Bath/Shower Valves. Deck mounted bath/shower transfer valves with integral backflow protection shall comply with ASME A112.18.1/CSA B125.1.

    This shall include handheld showers, and other bathing appliances mounted on the deck of bathtubs or other bathing appliances that incorporate a hose or pull out feature. 417.3 Handheld Showers. Handheld showers shall comply with ASME A112.18.1/CSA B125.1. Handheld showers with integral backflow protection shall comply with ASME A112.18.1/CSA B125.1 or shall have a backflow prevention device that complies with ASME A112.18.3 or ASSE 1014. 417.4 Faucets and Fixture Fittings with Hose Con- nected Outlets. Faucets and fixture fittings with pull out spout shall comply with ASME A112.18.1/CSA B125.1. Faucets and fixture fittings with pull out spouts with integral backflow protection shall comply with ASME A112.18.1/CSA B125.1 or shall have a backflow preventer device that complies with ASME A112.18.3. 417.5 Separate Controls for Hot and Cold Water. Where two separate handles control the hot and cold water, the left-hand control of the faucet where facing the fixture fitting outlet shall control the hot water. Faucets and diverters shall be connected to the water distribution system so that hot water corresponds to the left side of the fixture fitting.

    Single-handle mixing valves installed in showers and tub-shower combinations shall have the flow of hot water corresponding to the markings on the fixture fitting. 417.6 Low-Pressure Water Dispenser. Beverage faucets shall comply with ASME A112.18.1/CSA B125.1. Electrically heated or cooled water dispensers shall comply with ASSE 1023.

    417.7 Head Shampoo Sink Faucets. Head shampoo sink faucets shall be supplied with hot water that is limited to not more than 120°F (49°C). Each faucet shall have integral check valves to prevent crossover flow between the hot and cold water supply connections. The means for regulating the maximum temperature shall be in accordance with one of the following:

    (1) A limiting device conforming to ASSE 1070/ASME A112.1070/CSA B125.70.

    (2) A water heater conforming to ASSE 1084.

    (3) A temperature-actuated, flow-reduction device conforming to ASSE 1062. 417.8 Footbaths and Pedicure Baths. The water supplied to specialty plumbing fixtures, such as pedicure chairs having an integral foot bathtub and footbaths, shall be limited to not more than 120ºF (49ºC) by a water-temperaturelimiting device that conforms to ASSE 1070/ASME A112.1070/CSA B125.70 or by a water heater complying with ASSE 1084.

    418.0 Floor Drains.

  • CPC § 3.5.2 High relevance — show source text

    pump.

    R309.3.5.2 Required capacity. The water supply shall have the capacity to provide the required design flow rate for sprinklers for a period of time as follows:

    1. Seven minutes for dwelling units one story in height and less than 2,000 square feet (186 m [2] ) in area. For the purpose of determining the area of the dwelling unit, the area of attached garages and attached open carports, porches, balconies and patios shall not be included.
    2. Ten minutes for dwelling units two or more stories in height or equal to or greater than 2,000 square feet (186 m [2] ) in area. For the purpose of determining the area of the dwelling unit, the area of attached garages and attached open carports, porches, balconies and patios shall not be included.

    R309.3.5.2.1 Where a well system, a water supply tank system or a combination thereof is used, the configuration for the system shall be one of the following: 1. The water supply shall serve both domestic and fire sprinkler systems. Any combination of well capacity and tank storage shall be permitted to meet the capacity requirement. 2. A stand-alone tank is permitted if the following conditions are met: 2.1. The pump shall be connected to a 220-volt circuit breaker shared with a common household appliance (e.g., range, oven, dryer), 2.2. The pump shall be a stainless steel 240-volt pump, 2.3. A valve shall be provided to exercise the pump. The discharge of the exercise valve shall be piped to the tank, and

    2.4. A sign shall be provided stating “Valve must be opened monthly for 5 minutes.” 2.5. A means for automatically refilling the tank level so that the tank capacity will meet the required water supply duration in minutes shall be provided.

    R309.3.5.3 Connections to automatic fire sprinkler systems. The potable water supply to automatic fire sprinkler shall be protected against backflow by a double check backflow prevention assembly, a double check fire protection backflow prevention assembly, a reduced pressure principle backflow prevention assembly or a reduced pressure principle fire protection backflow prevention assembly.

    Exception: Where permitted by Section R309.3.1.1, backflow protection for the water supply system shall not be required.

    R309.3.5.3.1 Additives or nonpotable source. Where systems contain chemical additives or antifreeze, or where systems are connected to a nonpotable secondary water supply, the potable water supply shall be protected against backflow by a reduced pressure principle backflow prevention assembly or a reduced pressure principle fire protection backflow prevention assembly. Where chemical additives or antifreeze is added to only a portion of an automatic sprinkler or standpipe system, the reduced pressure principle fire protection backflow preventer shall be permitted to be located so as to isolate that portion of the system.

    R309.3.6 Pipe sizing. The piping to sprinklers shall be sized for the flow required by Section R309.3.4.2. The flow required to supply the plumbing fixtures shall not be required to be added to the sprinkler design flow.

  • CPC § 603.5.14.2 High relevance — show source text

    (1) Reduced pressure principle backflow prevention assembly (RP)

    (2) Reduced pressure detector fire protection backflow prevention assembly

    Nonpotable water sources include fire department vehicles carrying water of questionable quality or water that is treated with antifreeze, corrosion inhibitors, or extinguishing agents. 603.5.14.2 Chemicals. Where antifreeze, corrosion inhibitors, or other chemicals are added to a fire protection system supplied from a potable water supply, the potable water system shall be protected by one of the following:

    (1) Reduced pressure principle backflow prevention assembly (RP)

    (2) Reduced pressure detector fire protection backflow prevention assembly 603.5.14.3 Hydraulic Design. Where a backflow device is installed in the potable water supply to a fire protection system, the hydraulic design of the system shall account for the pressure drop through the backflow device. Where such devices are retrofitted for an existing fire protection system, the hydraulics of the sprinkler system design shall be checked to verify that there will be sufficient water pressure available for satisfactory operation of the fire sprinklers. 603.5.15 Health Care or Laboratory Areas. Vacuum breakers for washer-hose bedpans shall be located not less than 5 feet (1524 mm) above the floor. Hose con

    nections in health care or laboratory areas shall be not less than 6 feet (1829 mm) above the floor. 603.5.16 Special Equipment. Portable cleaning equipment and dental vacuum pumps shall be protected from backflow by an air gap, an atmospheric vacuum breaker, a spill-resistant vacuum breaker, or a reduced pressure principle backflow preventer.

    603.5.17 Potable Water Outlets and Valves. Potable water outlets, freeze-proof yard hydrants, combination stop-and-waste valves, or other fixtures that incorporate a stop and waste feature that drains into the ground shall not be installed underground. 603.5.18 Pure Water Process Systems. The water supply to a pure water process system, such as dialysis water systems, semiconductor washing systems, and similar process piping systems, shall be protected from backpressure and backsiphonage by a reduced-pressure principle backflow preventer. 603.5.18.1 Dialysis Water Systems. The individual connections of the dialysis related equipment to the dialysis pure water system shall not require additional backflow protection. 603.5.19 Garbage Can Washers. Where garbage can washers are connected to a potable water supply system, the connection shall be protected against backflow in accordance with Table 603.2.

    603.5.20 Plumbing Fixture Fittings. Plumbing fixture fittings with integral backflow protection shall comply with ASME A112.18.1/CSA B125.1. 603.5.21 Swimming Pools, Spas, and Hot Tubs. Potable water supply to swimming pools, spas, and hot tubs shall be protected by an air gap or a reduced pressure principle backflow preventer in accordance with the following:

    (1) The unit is equipped with a submerged fill line.

    (2) The potable water supply is directly connected to the unit circulation system. 603.5.22 Chemical Dispensers. The water supply to chemical dispensers shall be protected against backflow by one of the following:

  • CPC § 3.5.3 High relevance — show source text

    2.4. A sign shall be provided stating “Valve must be opened monthly for 5 minutes.” 2.5. A means for automatically refilling the tank level so that the tank capacity will meet the required water supply duration in minutes shall be provided.

    R309.3.5.3 Connections to automatic fire sprinkler systems. The potable water supply to automatic fire sprinkler shall be protected against backflow by a double check backflow prevention assembly, a double check fire protection backflow prevention assembly, a reduced pressure principle backflow prevention assembly or a reduced pressure principle fire protection backflow prevention assembly.

    Exception: Where permitted by Section R309.3.1.1, backflow protection for the water supply system shall not be required.

    R309.3.5.3.1 Additives or nonpotable source. Where systems contain chemical additives or antifreeze, or where systems are connected to a nonpotable secondary water supply, the potable water supply shall be protected against backflow by a reduced pressure principle backflow prevention assembly or a reduced pressure principle fire protection backflow prevention assembly. Where chemical additives or antifreeze is added to only a portion of an automatic sprinkler or standpipe system, the reduced pressure principle fire protection backflow preventer shall be permitted to be located so as to isolate that portion of the system.

    R309.3.6 Pipe sizing. The piping to sprinklers shall be sized for the flow required by Section R309.3.4.2. The flow required to supply the plumbing fixtures shall not be required to be added to the sprinkler design flow.

    R309.3.6.1 Method of sizing pipe. Piping supplying sprinklers shall be sized using the prescriptive method in Section R309.3.6.2 or by hydraulic calculation in accordance with NFPA 13D. The minimum pipe size from the water supply source to any sprinkler shall be [3] / 4 inch (19 mm) nominal. Threaded adapter fittings at the point where sprinklers are attached to the piping shall be not less than [1] / 2 inch (13 mm) nominal.

    R309.3.6.2 Prescriptive pipe sizing method. Pipe shall be sized by determining the available pressure to offset friction loss in piping and identifying a piping material, diameter and length using the equation in Section R309.3.6.2.1 and the procedure in Section R309.3.6.2.2 .

    2025 CALIFORNIA RESIDENTIAL CODE 3-45

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    BUILDING PLANNING

    TABLE R309.3.6.2(1)—WATER SERVICE PRESSURE LOSS (PL ) a, b
    svc    		 Col2 Col3 Col4 Col5 Col6 Col7 Col8 Col9 Col10 Col11 Col12 Col13
    FLOW
    RATEc
    (gpm)    		 3/4-INCH WATER SERVICE
    PRESSURE LOSS (psi)    		 3/4-INCH WATER SERVICE
    PRESSURE LOSS (psi)    		 3/4-INCH WATER SERVICE
    PRESSURE LOSS (psi)    		 **3/4-INCH
  • CPC § 602.0 High relevance — show source text

    602.0 Unlawful Connections.

    602.1 Prohibited Installation. No installation of potable water supply piping, or part thereof, shall be made in such a manner that it will be possible for used, unclean, polluted, or contaminated water, mixtures, or substances to enter a portion of such piping from a tank, receptor, equipment, or plumbing fixture by reason of backsiphonage, suction, or other cause, either during normal use and operation thereof, or where such tank, receptor, equipment, or plumbing fixture is flooded or subject to pressure exceeding the operating pressure in the hot or cold water piping. 602.2 Cross-Contamination. No person shall make a connection or allow one to exist between pipes or conduits carrying domestic water supplied by a public or private building supply system, and pipes, conduits, or fixtures containing or carrying water from any other source or containing or carrying water that has been used for any purpose whatsoever, or piping carrying chemicals, liquids, gases, or substances whatsoever, unless there is provided a backflow prevention device approved for the potential hazard and maintained in accordance with this code. Each point of use shall be separately protected where potential cross-contamination of individual units exists.

    602.3 Backflow Prevention. No plumbing fixture, device, or construction shall be installed or maintained, or shall be connected to a domestic water supply, where such installation or connection provides a possibility of polluting such water supply or cross-connection between a distributing system of water for drinking and domestic purposes and water that becomes contaminated by such plumbing fixture, device, or construction unless there is provided a backflow prevention device approved for the potential hazard.

    602.4 Approval by Authority. No water piping supplied by a private water supply system shall be connected to any other source of supply without the approval of the Authority Having Jurisdiction, Health Department, or other department having jurisdiction.

    603.0 Cross-Connection Control.

    603.1 General. Cross-connection control shall be provided in accordance with the provisions of this chapter.

    No person shall install a water-operated equipment or mechanism, or use a water-treating chemical or substance, where it is found that such equipment, mechanism, chemical, or substance causes pollution or contamination of the domestic water supply. Such equipment or mechanism shall be permitted where equipped with an approved backflow prevention device or assembly.

    603.2 Approval of Devices or Assemblies. Before a device or an assembly is installed for the prevention of backflow, it shall have first been approved by the Authority Having Jurisdiction. Devices or assemblies shall be tested in accordance with recognized standards or other standards acceptable to the Authority Having Jurisdiction. Backflow prevention devices and assemblies shall comply with Table 603.2, except for specific applications and provisions as stated in Section 603.5.1 through Section 603.5.22.

    2025 CALIFORNIA PLUMBING CODE 139

    ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

    WATER SUPPLY AND DISTRIBUTION

  • CPC § 603.3 Medium relevance — show source text

    Testing or maintenance shall be performed by a certified backflow assembly tester or repairer certified in accordance with ASSE/IAPMO/ANSI Series 5000 or any other additional certification approved by the Authority Having Jurisdiction.

    603.3 Backflow Prevention Devices, Assemblies, and Methods. Backflow prevention devices, assemblies, and methods shall comply with Section 603.3.1 through Section 603.3.12.

    603.3.1 Air Gap. The minimum air gap to afford backflow protection shall be in accordance with Table 603.3.1. 603.3.2 Atmospheric Vacuum Breaker (AVB). An atmospheric vacuum breaker consists of a body, a checking member, and an atmospheric port.

    603.3.3 Hose Connection Backflow Preventer. A hose connection backflow preventer consists of two independent check valves with an independent atmospheric vent between and a means of field testing and draining.

    603.3.4 Double Check Valve Backflow Prevention Assembly (DC). A double check valve backflow prevention assembly consists of two independently acting internally loaded check valves, four properly located test cocks, and two isolation valves.

    603.3.5 Pressure Vacuum Breaker Backflow Pre- vention Assembly (PVB). A pressure vacuum breaker backflow prevention assembly consists of a loaded air inlet valve, an internally loaded check valve, two properly located test cocks, and two isolation valves. This device shall be permitted to be installed indoors where provisions for spillage are provided. 603.3.6 Spill-Resistant Pressure Vacuum Breaker (SVB). A pressure-type vacuum breaker backflow prevention assembly consists of one check valve force loaded closed and an air inlet vent valve force loaded open to atmosphere, positioned downstream of the check valve and located between and including two tightly closing shutoff valves and test cocks. 603.3.7 Reduced-Pressure Principle Backflow Prevention Assembly (RP). A reduced-pressure principle backflow prevention assembly consists of two independently acting internally loaded check valves, a differential pressure relief valve, four properly located test cocks, and two isolation valves.

    603.3.8 Double Check Detector Fire Protection Backflow Prevention Assembly. A double check valve backflow prevention assembly with a parallel

    detector assembly consisting of a water meter and a double check valve backflow prevention assembly (DC).

    603.3.9 Reduced Pressure Detector Fire Protec- tion Backflow Prevention Assembly. A reducedpressure principle backflow prevention assembly with a parallel detector assembly consisting of a water meter and a reduced-pressure principle backflow prevention assembly (RP).

    603.3.10 Dual Check Backflow Preventer. A dual check backflow preventer consists of two independently acting check valves, force loaded to a normally closed position.

    603.3.11 Laboratory Faucet Backflow Preven- ters. Laboratory faucet backflow preventers shall comply with ASSE 1035.

    603.3.12 Backflow Preventer with Intermediate Atmospheric Vent. A backflow preventer with intermediate atmospheric vent consists of two independently acting check valves, force loaded to a normally closed position, and an intermediate chamber with a means for automatically venting to atmosphere, force loaded to a normally open position. 603.4 General Requirements. Assemblies shall comply with listed standards and be acceptable to the Authority Having Jurisdiction, with jurisdiction over the selection and installation of backflow prevention assemblies.

    **603.4.1 Backflow Prevention Valve.

  • CPC § 603.5.6.1 Medium relevance — show source text

    (1) Atmospheric vacuum breaker (AVB)

    (2) Pressure vacuum breaker backflow prevention assembly (PVB)

    (3) Spill-resistant pressure vacuum breaker (SVB)

    (4) Reduced-pressure principle backflow prevention assembly (RP)

    (5) A valve complying with IAPMO PS 72 603.5.6.1 Systems with Pumps. Where sprinkler and irrigation systems have pumps, connections for pumping equipment, or auxiliary air tanks, or are otherwise capable of creating backpressure, the potable water supply shall be protected by the following type of device where the backflow device is located upstream from the source of backpressure:

    (1) Reduced-pressure principle backflow prevention assembly (RP) 603.5.6.2 Systems with Backflow Devices. Where systems have a backflow device installed downstream from a potable water supply pump or a potable water supply pump connection, the device shall be one of the following:

    (1) Atmospheric vacuum breaker (AVB)

    (2) Pressure vacuum breaker backflow prevention assembly (PVB)

    (3) Spill-resistant pressure vacuum breaker (SVB)

    (4) Reduced-pressure principle backflow prevention assembly (RP) 603.5.6.3 Systems with Chemical Injectors. Where systems include a chemical injector or provisions for chemical injection, the potable water supply shall be protected by a reduced-pressure principle backflow prevention assembly (RP).

    2025 CALIFORNIA PLUMBING CODE 141

    ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

    WATER SUPPLY AND DISTRIBUTION

    TABLE 603.2 BACKFLOW PREVENTION DEVICES, ASSEMBLIES, AND METHODS Col2 Col3 Col4 Col5 Col6 Col7
    DEGREE OF HAZARD DEGREE OF HAZARD DEGREE OF HAZARD DEGREE OF HAZARD DEGREE OF HAZARD DEGREE OF HAZARD DEGREE OF HAZARD
    DEVICE, ASSEMBLY,
    OR METHOD1    		 APPLICABLE
    STANDARDS    		 POLLUTION
    (LOW HAZARD)    		 POLLUTION
    (LOW HAZARD)    		 CONTAMINATION
    (HIGH HAZARD)    		 CONTAMINATION
    (HIGH HAZARD)    		 INSTALLATION2,3
    DEVICE, ASSEMBLY,
    OR METHOD1    		 APPLICABLE
    STANDARDS    		 BACK-
    SIPHONAGE    		 BACK-
    PRESSURE    		 BACK-
    SIPHONAGE    		 BACK-
    PRESSURE    		 BACK-
    PRESSURE
    Air gap ASME
    A112.1.2    		 X –– X –– See Table 603.3.1 in this chapter.
    Air gap fittings for use
    with plumbing fixtures,
    appliances, and appurte-
    nances    		 ASME
    A112.1.3    		 X –– X –– Air gap fitting is a device with an internal air
    gap, and typical installation includes
    plumbing fixtures, appliances,
  • CPC § 4.33 Medium relevance — show source text

    [MP] BACKFLOW PREVENTER. A backflow prevention assembly, a backflow prevention device or other means or method to prevent backflow into the potable water supply.

    [MP] BACKFLOW PREVENTER, REDUCED-PRESSURE-ZONE TYPE. A backflow-prevention device consisting of two independently acting check valves, internally force loaded to a normally closed position and separated by an intermediate chamber (or zone) in which there is an automatic relief means of venting to atmosphere internally loaded to a normally open position between two tightly closing shutoff valves and with means for testing for tightness of the checks and opening of relief means.

    [MP] BACKPRESSURE. Pressure created by any means in the water distribution system that by being in excess of the pressure in the water supply mains causes a potential backflow condition.

    [MP] BACKPRESSURE, LOW HEAD. A pressure less than or equal to 4.33 psi (29.88 kPa) or the pressure exerted by a 10-foot (3048 mm) column of water.

    2-6 2025 CALIFORNIA RESIDENTIAL CODE

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    DEFINITIONS

    [MP] BACKSIPHONAGE. The flowing back of used or contaminated water from piping into a potable water-supply pipe due to a negative pressure in such pipe.

    [MP] BACKWATER VALVE. A device installed in a drain or pipe to prevent backflow of sewage.

    [MP] BALANCED VENTILATION SYSTEM. A ventilation system that simultaneously supplies outdoor air to and exhausts air from a space, where the mechanical supply airflow rate and the mechanical exhaust airflow rate are within 10 percent of the average of the two airflow rates.

    [RB] BASEMENT. A story that is not a story above grade plane (see “Story above grade plane”).

    [RB] BASIC WIND SPEED. Three-second gust speed at 33 feet (10 058 mm) above the ground in Exposure C (see Section R301.2.1) as given in Figure R301.2(2).

    [MP] BATHROOM GROUP. A group of fixtures, including or excluding a bidet, consisting of a water closet, lavatory, and bathtub or shower. Such fixtures are located together on the same floor level.

    BEDRIDDEN PERSON. A person, requiring assistance in turning and repositioning in bed, or being unable to independently transfer to and from bed, except in facilities with appropriate and sufficient care staff, mechanical devices if necessary and safety precautions as deter- mined in Title 22 regulations, by the Director of Social Services or his or her designated representative. Persons who are unable to independently transfer to and from bed, but who do not need assistance to turn or reposition in bed, shall be considered nonambulatory.

    The Director of Social Services or his or her designated representative shall make the determination of the bedridden status of persons with developmental disabilities, in consultation with the Director of Developmental Services or his or her designated representative.

    The Director of Social Services or his or her designated representative shall make the determination of the bedridden status of all other persons with disabilities who are not developmentally disabled.

    [MP] BEND. A drainage fitting, designed to provide a change in direction of a drain pipe of less than the angle specified by the amount necessary to establish the desired slope of the line (see “Elbow” and “Sweep”).

  • CPC § 207.0 Medium relevance — show source text

    2025 CALIFORNIA PLUMBING CODE 31

    ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

    DEFINITIONS

    as otherwise provided by statute, to have adequate personnel and expertise to carry out the testing of systems, materials, and construction fixtures or appliances. Area Drain. A receptor designed to collect surface or storm water from an open area. Aspirator. A fitting or device supplied with water or other fluid under positive pressure that passes through an integral orifice or constriction, causing a vacuum. Authority Having Jurisdiction. The organization, office, or individual responsible for enforcing the requirements of a code or standard, or for approving equipment, materials, installations, or procedures. The Authority Having Jurisdiction shall be a federal, state, local, or other regional department or an individual such as a plumbing official, mechanical official, labor department official, health department official, building official, or others having statutory authority. In the absence of statutory authority, the Authority Having Jurisdiction may be some other responsible party. This definition shall include the Authority Having Jurisdiction’s duly authorized representative.

    [HCD 1 & HCD 2] “Authority Having Jurisdiction” shall mean “Enforcing Agency” as defined in Section 207.0 of this code.

    204.0 – B –

    Backflow. The flow of water or other liquids, mixtures, or substances into the distributing pipes of a potable supply of water from sources other than its intended source. See Backpressure Backflow and Backsiphonage. Backflow Connection. An arrangement whereby backflow

    can occur.

    Backflow Preventer. A backflow prevention device, an assembly, or another method to prevent backflow into the potable water system. Backpressure Backflow. Backflow due to an increased pressure above the supply pressure, which may be due to pumps, boilers, gravity, or other sources of pressure. Backsiphonage. The flowing back of used, contaminated, or polluted water from a plumbing fixture or vessel into a water supply pipe due to a pressure less than atmospheric in such pipe. See Backflow. Backwater Valve. A device installed in a drainage system to prevent reverse flow.

    Bathroom. A room equipped with a shower, bathtub, or combination bath/shower.

    Bathroom, Half. A room equipped with only a water closet and lavatory. Bathroom Group. Any combination of fixtures, not to exceed one water closet, two lavatories, either one bathtub or one combination bath/shower, and one shower, and may include a bidet and an emergency floor drain. Battery of Fixtures. A group of two or more similar, adjacent fixtures that discharge into a common horizontal waste or soil branch.

    Bedpan Steamer. A fixture that is used to sterilize bedpans by way of steam.

    Body Spray. A shower device for spraying water onto a bather from other than the overhead position.

    Boiler Blowoff. An outlet on a boiler to permit emptying or discharge of sediment.

Frequently asked questions

Do §§ 402.7 and 402.9 require a specific device at every fixture?

No — § 402.7 requires that the supply lines and fittings prevent backflow in accordance with Chapter 6; Chapter 6 (603.x and Table 603.2) prescribes the acceptable device/method for a given hazard or fixture. The CPC does not name a single device for all cases — it points you to Chapter 6 for device selection.

Can a manufacturer’s integral backflow feature be accepted in lieu of a separate device?

Yes — fixtures or fittings with integral backflow preventers or integral air gaps installed per their listing and manufacturer’s instructions are acceptable, provided the installation follows the listing and the CPC’s Chapter 6 requirements.

What does “must not be compromised by the designated fixture fitting mounting surface” mean?

It means you cannot install or mount a fixture in a way that blocks, disables, or otherwise renders the required backflow prevention ineffective or inaccessible. The CPC requires installers to maintain the integrity of the backflow protection when placing the fixture. § 402.9.

If I install a pull‑out faucet for a sink in a café, which code paragraphs should I check?

Start with § 402.7 and § 402.9, then consult Chapter 6 (603.x) for backflow device selection and the faucet/fixture text that references ASME A112.18.1 and ASME A112.18.3 for pull‑out or hose‑type fittings.

Are there location limits for backflow devices (e.g., pits, outdoors)?

Yes — Chapter 6 prohibits installation of devices with atmospheric vents/ports in pits, underground, or submerged locations and restricts locations with toxic/corrosive fumes. See Chapter 603 general requirements.

More in California Plumbing Code

Ask about the CPC

Get cited, plain-English answers on the California Plumbing Code for your project — any code section, any scenario.

Start Free Trial

Related in the CPC

How must fixtures be installed and secured (wall‑hung, floor‑mounted, closet flanges)?

When are slip‑joint connections required to be accessible and what access is required?

Fixture installation, securing, and supply/drain connections

California Plumbing Code