Landscaping (C-27) · Lesson 4 of 7

Backflow Protection for an Irrigation Supply (CPC Sec. 603)

"Backflow Protection for an Irrigation Supply (CPC Sec. 603)" is lesson 4 of 7 in the Landscaping (C-27) Learning Hub. It opens with "Why the Irrigation Supply Is a Cross-Connection" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. Why the Irrigation Supply Is a Cross-Connection
  2. Pick the Device by System Type - CPC Sec. 603.5.6
  3. Mounting Height and Position - Table 603.2
  4. Access, Clearance, and the 5-Foot Platform Rule
  5. Testing Is Not Optional

The worked example in the course applies this lesson to a realistic job in 3 steps, starting with "Check clearance and platform".

What you'll be able to do

  • Explain the main idea of "Backflow Protection for an Irrigation Supply (CPC Sec. 603)" in plain language you can use on the exam.
  • Apply this step with confidence: "Mounting Height and Position - Table 603.2".
  • Apply this step with confidence: "Access, Clearance, and the 5-Foot Platform Rule".
  • Apply this step with confidence: "Testing Is Not Optional".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Backflow Protection for an Irrigation SupplySITE 1 ELEVATION (PVB)PVBto valves and headsraisedplanter12 in. min.30 in.42 in.to PVBSITE 1: no pump, no injectorAVB, PVB, SVB, RP or IAPMO PS 72 valve(CPC 603.5.6)SITE 2: booster pump (backpressure)Upstream of pump: RP only (603.5.6.1)Downstream: AVB, PVB, SVB or RP (603.5.6.2)SITE 3: chemical injectorRP only (CPC 603.5.6.3)Test at install, repair, relocationand at least annually (CPC 603.4.2)Mount per listing and manufacturer (603.4.3)Table 603.2 height above downstream piping: AVB 6 in. | PVB 12 in. | SVB 12 in. | RP horizontalCPC 603.4.3: 12 in. under assembly to grade; platform if installed more than 5 ft above gradePVB: 30 in. highest piping + 12 in. = 42 in. above grade42 in. is under 60 in.: no platform neededSource: 2025 California Plumbing Code Sec. 603.1-603.5.6.3, Table 603.2, Sec. 610.13(6); MWELO Sec. 492.7(a)(1)(F).CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: Why the Irrigation Supply Is a Cross-Connection

A sprinkler system can pull soil water, fertilizer or pump pressure back into the drinking-water line. The 2025 California Plumbing Code (CPC) Sec. 603.1 says no water-operated equipment may be installed where it can contaminate the domestic supply unless it has an approved backflow prevention device or assembly, and Sec. 603.2 requires the Authority Having Jurisdiction to approve the device before it is installed. MWELO Sec. 492.7(a)(1)(F) independently requires backflow prevention on every irrigation system and sends you to local code for more. The piping on the irrigation side is not sized by the CPC if it is separated by an approved air gap or backflow device, but the potable supply feeding it must be sized for the full connected domestic plus irrigation demand (CPC Sec. 610.13, item 6).

Step 2: Pick the Device by System Type - CPC Sec. 603.5.6

Sec. 603.5.6 sorts irrigation supplies three ways. No pump, no pump connection and no chemical injection: protect with an atmospheric vacuum breaker (AVB), pressure vacuum breaker assembly (PVB), spill-resistant pressure vacuum breaker (SVB), reduced-pressure principle assembly (RP), or a valve complying with IAPMO PS 72. A system with a pump, a pump connection or auxiliary air tank (anything that can create backpressure): the device upstream of the source of backpressure must be an RP (Sec. 603.5.6.1); a device installed downstream of the pump may be an AVB, PVB, SVB or RP (Sec. 603.5.6.2). A system with a chemical injector or provision for one: an RP (Sec. 603.5.6.3).

The remaining 3 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.

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