Building Code Glossary
Water Supply System: Building Code Definition
How the IPC 2009 define water supply system, where the wording differs, and which chapters depend on the term.
On this page
Last updated September 7, 2026 · 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.
Direct answer
Water supply system is a defined term in the International Plumbing Code (IPC) 2009, in Definitions. The code's own words are: “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.” No other I-Code in this corpus defines it, so the IPC 2009 definition is the one to work from. The term is used in 10 chapters of this corpus, most often in Water Supply and Distribution (IPC 2009), Water Supply and Distribution (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. 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, Harth founder and architectural technology specialist · Published 2026-09-07 · Updated 2026-09-07.
What does this term mean?
Water Supply System — IPC 2009, Definitions:
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.
What must be verified before using this guidance?
Water Supply System is defined once in this corpus, in the Definitions chapter of the International Plumbing Code (IPC) 2009:
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.
Where water supply system is used in the code
The term appears in 10 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 | IPC 2009 | 38 |
| Water Supply and Distribution | IRC 2009 | 11 |
| Definitions | IPC 2009 | 6 |
| General Regulations | IPC 2009 | 6 |
| Water Heaters | IPC 2009 | 3 |
| Building Planning | IRC 2009 | 2 |
| Fuel Gas | IRC 2009 | 2 |
| General Plumbing Requirements | IRC 2009 | 2 |
| Fire Service Features | IFC 2009 | 1 |
| Fixtures, Faucets and Fixture Fittings | IPC 2009 | 1 |
The term in use
How the code actually writes about water supply system, 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.
A potable water supply system shall be designed and installed as to prevent contamination from nonpotable liquids, solids or gases being introduced into the potable water supply.
Every plumbing fixture, device or appliance requiring or using water for its proper operation shall be directly or indirectly connected to the water supply system in accordance with the provisions of this code.
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 (IPC 2009) | distribution, structure |
| Water-supply System (IRC 2009) | distributing, building |
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:
- Structure — IPC 2009: That which is built or constructed or a portion thereof.
- Premises — IMC 2009: A lot, plot or parcel of land, including any structure thereon.
- Control — 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 — 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 and the ICC adoption maps cover the middle rows.
| Check | Where | Confirmed |
|---|---|---|
| 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 | Water Supply and Distribution (IRC 2009) | |
| Re-check the requirement that uses it | Definitions (IPC 2009) | |
| Re-check the requirement that uses it | General Regulations (IPC 2009) | |
| Confirm the dependent definition | Structure | |
| 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
- Structure: Building Code Definition
- Premises: Building Code Definition
- Service: Building Code Definition
- Control: Building Code Definition
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 publishes the current model text and the ICC adoption maps show which edition a jurisdiction has adopted; those sources control.
Source links
Frequently asked questions
What is the code definition of water supply system?
The International Plumbing Code (IPC) 2009 defines it in Definitions 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.” 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 10 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 a water supply system?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IPC 2009 states, in Definitions: “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.” It is defined in 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 does IPC mean in plumbing?
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 IPC 2009 defines 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.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.
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