# Water-supply System: Building Code Definition

> How the IRC 2009 define water-supply system, where the wording differs, and which chapters depend on the term.

- Canonical: https://harth.build/resources/glossary/water-supply-system-code-term/
- 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 (2009 editions transcribed in this corpus) |
| Primary source | IRC 2009 Definitions (model text, not a jurisdiction's adopted text) |
| Chapters using the term | 4 (counted across the codes hosted here) |
| Wording identical across codes | Single code (compare before citing one code's wording under another) |

## Direct answer

Water-supply system is a defined term in the International Residential Code (IRC) 2009, in Definitions. The code's own words are: “The water-service pipe, the water-distributing pipes and the necessary connecting pipes, fittings, control valves and all appurtenances in or adjacent to the building or premises.” No other I-Code in this corpus defines it, so the IRC 2009 definition is the one to work from. The term is used in 4 chapters of this corpus, most often in Water Supply and Distribution (IRC 2009), Plumbing Administration (IRC 2009), Marinas (IFC 2009). These pages transcribe the 2009 model text; verify the definition against the edition and amendments your authority having jurisdiction has adopted. Record the jurisdiction, the adopted edition, the application date and any local amendment that rewrites the definition before you use it on a live project, because a term redefined by amendment changes every requirement that depends on it.

*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?

**Water-supply System** — IRC 2009, Definitions:

> The water-service pipe, the water-distributing pipes and the necessary connecting pipes, fittings, control valves and all appurtenances in or adjacent to the building or premises.

![Labeled code-term definition diagram: Water-supply System: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/water-supply-system-code-term/diagram-1344.webp)

*How the IRC 2009 define water-supply system, where the wording differs, and which chapters depend on the term.*

## What must be verified before using this guidance?

**Water-supply System** is defined once in this corpus, in the [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) chapter of the International Residential Code (IRC) 2009:

> The water-service pipe, the water-distributing pipes and the necessary connecting pipes, fittings, control valves and all appurtenances in or adjacent to the building or premises.

## Where water-supply system is used in the code

The term appears in 4 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/maryland/irc-2009/water-supply-and-distribution.md) | IRC 2009 | 3 |
| [Plumbing Administration](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/plumbing-administration.md) | IRC 2009 | 2 |
| [Marinas](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/marinas.md) | IFC 2009 | 1 |
| [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | IRC 2009 | 1 |

### The term in use

How the code actually writes about water-supply system, quoted from the 2009 text hosted here:

> Pipe and fittings used in the water-supply system shall have a maximum of 8 percent lead.

— [IRC 2009 §P2905.2](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/water-supply-and-distribution.md)

> Upon completion of the water-supply system or a section ofit, the system or portion completed shall be tested and proved tight under a water pressure of not less than the working pressure of the system or, for piping systems other than plastic, by an air test of not less than 50 psi (345 kPa).

— [IRC 2009 §P2503.7](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/plumbing-administration.md)


## Water-supply System compared with Water Supply System

These two are the closest pair in the 2009 I-Codes: about 82 per cent of their defining words are the same. The code states both and compares neither, so the difference is worth naming.

| | Wording unique to it |
| --- | --- |
| **Water-supply System** (IRC 2009) | distributing, building |
| [Water Supply System](https://harth.build/resources/glossary/water-supply-system.md) (IPC 2009) | distribution, structure |

Everything else in the two definitions is shared. If a project turns on which of the two applies, those words are the whole of the test — and a local amendment that edits one of them without editing the other moves the boundary between water-supply system and water supply system.

## The terms water-supply system is built out of

The definition above leans on 4 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what water-supply system covers:

- **[Building](https://harth.build/resources/glossary/building.md)** — IBC 2009: Any structure used or intended for supporting or sheltering any use or occupancy.
- **[Premises](https://harth.build/resources/glossary/premises.md)** — IMC 2009: A lot, plot or parcel of land, including any structure thereon.
- **[Control](https://harth.build/resources/glossary/control.md)** — IRC 2009: A manual or automatic device designed to regulate the gas, air, water or electrical supply to, or operation of, a mechanical system.
- **[Service](https://harth.build/resources/glossary/service.md)** — IRC 2009: The conductors and equipment for delivering energy from the serving utility to the wiring system of the premises served.

## Water-supply System: 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 | |
| Re-check the requirement that uses it | Water Supply and Distribution (IRC 2009) | |
| Re-check the requirement that uses it | Plumbing Administration (IRC 2009) | |
| Re-check the requirement that uses it | Marinas (IFC 2009) | |
| Re-check the requirement that uses it | Definitions (IRC 2009) | |
| Confirm the dependent definition | Building | |
| Confirm the dependent definition | Premises | |
| Confirm the dependent definition | Control | |
| 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)
- [Premises: Building Code Definition](https://harth.build/resources/glossary/premises.md)
- [Building: Building Code Definition](https://harth.build/resources/glossary/building.md)
- [Service: Building Code Definition](https://harth.build/resources/glossary/service.md)
- [Control: Building Code Definition](https://harth.build/resources/glossary/control.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 water-supply system?

The International Residential Code (IRC) 2009 defines it in Definitions as: “The water-service pipe, the water-distributing pipes and the necessary connecting pipes, fittings, control valves and all appurtenances in or adjacent to the building or premises.” 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 water-supply system?

In this corpus the term is used across 4 chapters, led by Water Supply and Distribution in the IRC 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 a water supply system?

Water Supply System is a separate defined term. The IPC 2009 defines it as: “The water service pipe, water distribution pipes, and the necessary connecting pipes, fittings, control valves and all appurtenances in or adjacent to the structure or premises.” That is not the same as water-supply system, which the IRC 2009 defines as “The water-service pipe, the water-distributing pipes and the necessary connecting pipes, fittings, control valves and all appurtenances in or adjacent to the building or premises.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.

### What is the IRC plumbing code?

Plumbing is a separate defined term. The IRC 2009 defines it as: “For the purpose of this code, plumbing refers to those installations, repairs, maintenance and alterations regulated by Chapters 25 through 33.” That is not the same as water-supply system, which the IRC 2009 defines as “The water-service pipe, the water-distributing pipes and the necessary connecting pipes, fittings, control valves and all appurtenances in or adjacent to the building or premises.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.

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