Containment vs. Isolation Backflow Protection: What California Requires
Containment protects the water system at the service connection; isolation protects at the hazard. How California's CCCPH treats each and when to use both.
Short answer: Containment backflow protection is an air gap or assembly at the customer’s service connection that keeps anything on the property from flowing back into the public water system. Isolation backflow protection is a device at a specific hazard inside the property, such as a boiler or irrigation line, that protects the building’s own plumbing. California’s Cross-Connection Control Policy Handbook (CCCPH) requires public water systems to protect against high hazard cross connections through premises containment (Section 3.2.2(c)), and accepts internal (isolation) protection in place of containment only with State Water Board approval when containment is not feasible (Section 3.2.2(c)(2)).
Last reviewed October 30, 2026, against the April 21, 2026 revision of the CCCPH. Sources are listed at the end.
What is containment backflow protection?
The CCCPH defines premises containment in Section 3.1.1 as protection of a public water system’s distribution system from backflow from a user’s premises, through one or more air gaps or backflow prevention assemblies installed as close as practical to the user’s service connection, in a way that isolates the user’s water supply from the public water system.
In plain terms: one device (or one per connection) at the property line, usually just after the meter, protects the public system from everything downstream. It does not need to know exactly where every hazard in the building is.
What is isolation backflow protection?
Isolation, often called internal protection or point-of-use protection, places a device at the hazard itself: a backflow preventer on a boiler feed, a vacuum breaker on an irrigation zone, an air gap at a chemical tank. Louisville Water, for example, describes an isolation device as one that protects a facility’s internal water supply from a hazard inside that facility and is located at the hazard.
The CCCPH does not define “isolation” as a separate term. It uses internal protection for protection inside the premises (Sections 3.2.2(c)(2) and 3.3.2(g)). Plumbing inside buildings is governed by the California Plumbing Code, which the CCCPH notes is outside the State Water Board’s authority except where it relates to public water systems (Chapter 2.3).
Containment vs. isolation at a glance
| Containment (premises containment) | Isolation (internal protection) | |
|---|---|---|
| Location | At or near the service connection, as close as practical | At the hazard inside the premises |
| What it protects | The public water system | The building’s internal plumbing and its occupants, and indirectly the public system |
| Who requires it | The public water system, under the CCCPH | Mostly the California Plumbing Code and local building officials; the PWS only when approved in lieu of containment |
| Who can inspect it | The water system, at the meter or property line | Requires access to the premises; if used instead of containment, the PWS must obtain that access (Section 3.3.2(g)) |
| Hazard knowledge needed | Low; covers unknown and future hazards on site | High; each hazard must be found and protected |
| Weakness | Does not protect people inside the building | One missed or added cross connection leaves the public system exposed |
| CCCPH default for high hazard | Required (Section 3.2.2(c)) | Allowed instead only with State Water Board approval (Section 3.2.2(c)(2)) |
What does the CCCPH require for containment?
Several sections work together:
- High hazard premises need containment. A water system must protect its distribution system from high hazard cross connections at all times through premises containment, using air gaps or RPs, unless the CCCPH provides otherwise (Section 3.2.2(c)).
- Location. Backflow protection must be as close as practical to the user’s service connection unless the water system approves one or more alternative locations (Section 3.3.2(g)).
- Air gaps at the service connection. The receiving container must be on the user’s premises at the service connection unless the water system approves another location, and any new air gap at a service connection must be reviewed and approved by the State Water Board before installation (Section 3.3.2(a)).
- Assemblies that cannot be used for containment. A spill-resistant vacuum breaker (SVB) may not be used for premises containment. A pressure vacuum breaker (PVB) may be used for containment only on roadway right-of-way irrigation where there is no backpressure potential (Section 3.3.2(e)).
- Alternate containment methods. With State Water Board approval, a water system may use an alternate containment method instead of a required air gap if it does not increase the risk to public health (Section 3.2.2(c)(1)).
When can isolation be used instead of containment?
Only through an approval path. Under Section 3.2.2(c)(2), after State Water Board review and approval, a water system may accept internal protection in lieu of containment when premises containment is not feasible. Section 3.3.2(g) then adds two conditions: the water system must obtain access to the premises, and it must make sure the on-site protection meets the CCCPH’s requirements for installation, field testing, and inspection.
That second condition is the practical hurdle. A water system that accepts internal protection takes on the job of tracking, testing, and inspecting devices inside a customer’s building, on the same annual schedule as any other assembly (Section 3.3.3).
The State Water Board’s change log for the April 2026 revision gives one example of how this path is used: a newly interconnected auxiliary water supply now needs either at least an RP for premises containment, or State Water Board-approved internal protection in lieu of containment.
When do you need both?
Often. The two approaches answer different questions, and the CCCPH expects some systems to run both:
- Noncommunity water systems. Schools, campuses, businesses, and other noncommunity systems own the premises they serve. The CCCPH says they must comply with both the California Plumbing Code and the CCCPH, may need internal cross-connection control programs within the premises, and must be able to enforce backflow protection within the premises. Where the two codes differ, the more protective minimum applies (Chapter 2.3).
- Non-testable internal devices. A noncommunity system’s plan must describe how it installs and maintains non-testable backflow preventers used for internal protection under the California Plumbing Code, and its tracking system must record their location and type (Sections 3.1.4(c)(5) and (c)(9)(C)).
- Water facilities. Facilities that produce, treat, store, or distribute drinking water, and water recycling plants, must have proper internal protection so that drinking water delivered to customers and workers at those facilities is free from unprotected cross connections (Section 3.2.2(g)).
- High hazard buildings. A hospital or laboratory has containment at the meter for the public system’s sake and isolation at its equipment for the occupants’ sake. The two are complementary, not substitutes.
The State Water Board’s plan template for small community systems asks the water system to state where backflow protection is required: at the meter or service connection only, internal, or both.
Who is responsible for each?
The CCCPH draws a clear line. The public water system must implement and enforce a cross-connection control program, but it “shall not be responsible for abatement of cross-connections which may exist within a user’s premises” (Section 3.1.3(a)). So:
- The water system decides, through its hazard assessment, what containment the premises needs, and enforces installation and testing.
- The customer installs, tests, and maintains the required assembly, and is responsible for the plumbing inside, including any isolation devices required by the plumbing code or local officials.
- When internal protection replaces containment, the water system must also gain access and verify that protection (Section 3.3.2(g)).
The water system is still expected to coordinate with plumbing, permitting, and health officials (Section 3.1.3(a)(10)), and a community water system’s plan must describe that coordination (Section 3.1.4(b)(13)).
A terminology trap in Appendix D
The CCCPH sometimes uses “isolated” or “isolation” to describe premises-level protection. Appendix D marks some high hazard items “(+) Premise isolated by air gap only,” and the April 2026 note on auxiliary water supplies allows an existing double check valve assembly “for premises isolation.” In both places the handbook means protection of the whole premises from the public system, which is containment in industry terms. When you read a CCCPH reference to isolation, check whether it means the premises or a single fixture before you design or approve anything.
Which approach fits common premises?
| Premises | Typical CCCPH starting point | Isolation role |
|---|---|---|
| Single-family home with lawn irrigation | Containment or protection on the irrigation service as set by the hazard assessment | Irrigation backflow device under local plumbing rules |
| Home with a private well | High hazard (Appendix D item 8): AG or RP containment, unless an existing pre-2024 DC meets the four conditions | Separation of well and potable piping inside |
| Car wash, laundry, dry cleaner | High hazard: AG or RP containment (Appendix D) | Devices at chemical dispensers and process equipment |
| Hospital, dialysis clinic, lab | High hazard: AG or RP containment (Appendix D) | Devices at equipment throughout the building |
| Business park on one meter | High hazard: AG or RP containment (Appendix D item 25) | Each tenant’s internal protection |
| School or campus that is its own water system | Internal program required under Chapter 2.3 | The main line of defense |
For the full hazard list, see high hazard vs. low hazard cross connections. For the basics, see what is a cross connection.
How Exodus helps
Exodus Water Services runs cross-connection control programs for public water systems across California from Thousand Oaks. Our certified Cross-Connection Control Specialists decide where containment is required, document any case for internal protection in a form the State Water Board can review, and track every containment and internal assembly in Exodus Water Compliance. Owners can read our backflow testing guide, and water systems can start with the CCCPH guide or the plan checklist.
Frequently asked questions
What is the difference between containment and isolation backflow protection? Containment protects the public water system with a device at the service connection. Isolation protects the building’s plumbing with a device at a specific hazard inside. Containment covers the whole premises; isolation covers one hazard.
Does California require containment or isolation? For high hazard premises, the CCCPH requires premises containment with an air gap or RP (Section 3.2.2(c)). Internal protection can replace containment only with State Water Board approval when containment is not feasible (Section 3.2.2(c)(2)).
Is isolation protection enough to protect the public water supply? Usually not by itself, because every hazard inside must be found and protected, and new ones can be added later. That is why the CCCPH makes containment the default for high hazard premises and requires the water system to gain access and verify any internal protection it accepts (Section 3.3.2(g)).
Who is responsible for internal backflow devices? The property owner, under the California Plumbing Code and local building officials. The water system is not responsible for abating cross connections within a premises (CCCPH Section 3.1.3(a)), unless it has accepted internal protection in lieu of containment.
Can a vacuum breaker be used for containment? A spill-resistant vacuum breaker cannot. A pressure vacuum breaker can be used for containment only on roadway right-of-way irrigation with no backpressure potential (CCCPH Section 3.3.2(e)).
Where must a containment assembly be installed? As close as practical to the user’s service connection, unless the water system approves another location (CCCPH Section 3.3.2(g)). RPs must sit 12 to 36 inches above grade unless the water system approves a different maximum height (Section 3.3.2(b)).
Do noncommunity water systems need internal programs? They may. The CCCPH says noncommunity systems must comply with both the California Plumbing Code and the CCCPH, may need internal cross-connection control programs, and must be able to enforce backflow protection within the premises (Chapter 2.3).
Last reviewed: October 30, 2026.
Sources
- State Water Board, Cross-Connection Control Policy Handbook page
- State Water Board, Cross-Connection Control Policy Handbook, April 2026 revision (PDF): Chapter 2.3, Sections 3.1.1, 3.1.3, 3.1.4, 3.2.2, 3.3.2, 3.3.3, and Appendix D
- State Water Board, Changes to the CCCPH, April 2026 change log (PDF)
- State Water Board, Small Community Water System CCC Plan template, v3 (PDF)
- Louisville Water, Cross-Connection Program FAQ: utility definition of containment and isolation devices
Not sure whether your program’s containment and internal protection rules match the CCCPH? Request a program review or call (805) 991-7333.