# Cross Connection: Building Code Definition

> How the IRC 2009, IPC 2009 define cross connection, where the wording differs, and which chapters depend on the term.

- Canonical: https://harth.build/resources/glossary/cross-connection/
- Last updated: 2026-09-07
- Data source: Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The [ICC code library](https://codes.iccsafe.org/codes) publishes the current model text and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) show which edition a jurisdiction has adopted; those sources control.

## Key facts

| Fact | Value |
| --- | --- |
| Defined in | IRC 2009, IPC 2009 (2009 editions transcribed in this corpus) |
| Primary source | IRC 2009 Definitions (model text, not a jurisdiction's adopted text) |
| Chapters using the term | 5 (counted across the codes hosted here) |
| Wording identical across codes | No (compare before citing one code's wording under another) |

## Direct answer

Cross connection is a defined term in the International Residential Code (IRC) 2009, in Definitions. The code's own words are: “Any connection between two otherwise separate piping systems whereby there may be a flow from one system to the other.” The IPC 2009 defines the same term with different wording, so the controlling text depends on which code governs the question in front of you — the comparison below sets the versions side by side. The term is used in 5 chapters of this corpus, most often in Water Supply and Distribution (IPC 2009), Special Piping and Storage Systems (IRC 2009), Definitions (IPC 2009). These pages transcribe the 2009 model text; verify the definition against the edition and amendments your authority having jurisdiction has adopted.

*Content and cited inputs reviewed by [Scott Barrington](https://nz.linkedin.com/in/barrington), Harth founder and architectural technology specialist · Published 2026-09-07 · Updated 2026-09-07.*

## What does this term mean?

**Cross Connection** — IRC 2009, Definitions:

> Any connection between two otherwise separate piping systems whereby there may be a flow from one system to the other.

![Labeled code-term definition diagram: Cross Connection: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/cross-connection/diagram-1344.webp)

*How the IRC 2009, IPC 2009 define cross connection, where the wording differs, and which chapters depend on the term.*

## What must be verified before using this guidance?

Two of the I-Codes in this corpus define **Cross Connection**, and the wording is not identical — read the version that governs your question.

| Code | Where it is defined | Definition |
| --- | --- | --- |
| IRC 2009 | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | Any connection between two otherwise separate piping systems whereby there may be a flow from one system to the other. |
| IPC 2009 | [Definitions](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/definitions.md) | Any physical connection or arrangement between two otherwise separate piping systems, one of which contains potable water and the other either water of unknown or questionable safety or steam, gas or chemical, whereby there exists the possibility for flow from one system to the other, with the direction of flow depending on the pressure differential between the two systems (see "Backflow"). |

## Where cross connection is used in the code

The term appears in 5 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.

| Chapter | Code | Mentions |
| --- | --- | --- |
| [Water Supply and Distribution](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/water-supply-and-distribution.md) | IPC 2009 | 4 |
| [Special Piping and Storage Systems](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/special-piping-and-storage-systems.md) | IRC 2009 | 3 |
| [Definitions](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/definitions.md) | IPC 2009 | 1 |
| [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | IRC 2009 | 1 |
| [Plumbing Fixtures](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/plumbing-fixtures.md) | IRC 2009 | 1 |

### The term in use

How the code actually writes about cross connection, quoted from the 2009 text hosted here:

> The use of solar energy shall not compromise the requirements for cross connection or protection of the potable water supply system required by this code.

— [IPC 2009 §601.2](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/water-supply-and-distribution.md)

> Cross connection of two supply tanks shall be permitted in accordance with Section M2203.6.

— [IRC 2009 §M2201.4](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/special-piping-and-storage-systems.md)

> Plumbing fIXtures shall be provided with an adequate supply of potable water to flush and keep the fIXtures in a clean and sanitary condition without danger of backflow or cross connection.

— [IRC 2009 §P2701.1](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/plumbing-fixtures.md)


## The terms cross connection is built out of

The definition above leans on 5 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what cross connection covers:

- **[Potable Water](https://harth.build/resources/glossary/potable-water.md)** — IRC 2009: Water free from impurities present in amounts sufficient to cause disease or harmful physiological effects and conforming in bacteriological and chemical quality to the requirements of the public health authority havingjurisdiction.
- **[Chemical](https://harth.build/resources/glossary/chemical.md)** — IFC 2009: An element, chemical compound or mixture of elements or compounds or both.
- **[Backflow](https://harth.build/resources/glossary/backflow.md)** — IPC 2009: Pressure created by any means in the water distribution system, which by being in excess ofthe pressure in the water supply mains causes a potential backflow condition.
- **[Piping](https://harth.build/resources/glossary/piping.md)** — IRC 2009: Where used in this code, “piping” refers to either pipe or tubing, or both.
- **[System](https://harth.build/resources/glossary/system.md)** — IFC 2009: An assembly of equipment consisting of a tank, container or containers, appurtenances, pumps, compressors and connecting piping.

## Cross Connection: what to open, and in what order

Every row is a document this term depends on. The [ICC code library](https://codes.iccsafe.org/codes) and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) cover the middle rows.

| Check | Where | Confirmed |
| --- | --- | --- |
| Read the definition in the adopted IRC | Definitions | |
| Read the definition in the adopted IPC | Definitions | |
| Re-check the requirement that uses it | Water Supply and Distribution (IPC 2009) | |
| Re-check the requirement that uses it | Special Piping and Storage Systems (IRC 2009) | |
| Re-check the requirement that uses it | Definitions (IPC 2009) | |
| Re-check the requirement that uses it | Definitions (IRC 2009) | |
| Confirm the dependent definition | Potable Water | |
| Confirm the dependent definition | Chemical | |
| Confirm the dependent definition | Backflow | |
| Local amendment to any of the above | Jurisdiction's amendment list | |

**A research aid, not a code determination.** The authority having jurisdiction decides which edition and which amendments apply.

## Where can you explore related guidance?

- [Explore all glossary guidance](https://harth.build/resources/glossary.md)
- [Potable Water: Building Code Definition](https://harth.build/resources/glossary/potable-water.md)
- [Chemical: Building Code Definition](https://harth.build/resources/glossary/chemical.md)
- [Backflow: Building Code Definition](https://harth.build/resources/glossary/backflow.md)
- [System: Building Code Definition](https://harth.build/resources/glossary/system.md)

## Sources and method

Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The [ICC code library](https://codes.iccsafe.org/codes) publishes the current model text and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) show which edition a jurisdiction has adopted; those sources control.

### Source links

- [codes.iccsafe.org](https://codes.iccsafe.org/codes)

- [iccsafe.org](https://www.iccsafe.org/advocacy/code-adoption-maps/)

## Frequently asked questions

### What is the code definition of cross connection?

The International Residential Code (IRC) 2009 defines it in Definitions as: “Any connection between two otherwise separate piping systems whereby there may be a flow from one system to the other.” The 2009 model text is reproduced here; the definition that binds your project is the one in the edition your jurisdiction has adopted, as amended locally.

### Which parts of the code depend on cross connection?

In this corpus the term is used across 5 chapters, led by Water Supply and Distribution in the IPC 2009. Those are the sections whose scope moves if the definition is amended locally, so read them together with Chapter 2 rather than on their own.

### What is considered a cross connection?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “Any connection between two otherwise separate piping systems whereby there may be a flow from one system to the other.” It is defined in IRC 2009, IPC 2009. Because it is a defined term, whatever the adopted edition says it means is what every section using it means — so check Chapter 2 of that edition and any local amendment before relying on this wording.

### What is the difference between backflow and cross-connection?

Backflow is a separate defined term. The IPC 2009 defines it as: “Pressure created by any means in the water distribution system, which by being in excess ofthe pressure in the water supply mains causes a potential backflow condition.” That is not the same as cross connection, which the IRC 2009 defines as “Any connection between two otherwise separate piping systems whereby there may be a flow from one system to the other.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.

### What is the purpose of a cross connection control program?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “Any connection between two otherwise separate piping systems whereby there may be a flow from one system to the other.” It is defined in IRC 2009, IPC 2009. It is not the same as Control, which the IRC 2009 defines separately as “A manual or automatic device designed to regulate the gas, air, water or electrical supply to, or operation of, a mechanical system.” Because it is a defined term, whatever the adopted edition says it means is what every section using it means — so check Chapter 2 of that edition and any local amendment before relying on this wording.

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