Section 604.1/Water Supply System Design
IPC 604 covers water supply system sizing including minimum pipe sizes, pressure, flow rates, and design methodology.
The water supply system must deliver water to all fixtures and equipment at the minimum flow rate and pressure required for proper operation. The design must account for peak demand, friction losses through piping, elevation changes, and the available supply pressure. Minimum pipe sizes are specified in Table 604.3 based on the fixture type. The total demand is calculated using water supply fixture units (WSFU) and converting to flow rate via Table 604.4.
Why this section exists
An undersized water supply system results in inadequate pressure and flow at fixtures, especially during peak demand. Low pressure causes poor fixture performance (weak showers, slow-filling toilets) and can prevent safety devices like backflow preventers from operating correctly. The sizing method ensures the system delivers adequate water to every fixture under worst-case simultaneous demand conditions.
What plan reviewers look for
Plan reviewers check the plumbing riser diagram and piping layout for pipe sizes. They verify that a water supply calculation is provided showing the total fixture unit count, the converted flow demand, the available vs. required pressure, and the pipe sizing methodology. They also check that the building supply pipe and meter are sized for the total demand.
Common violations
Related IPC requirements
Table 604.3 provides minimum pipe sizes by fixture type. Table 604.4 converts fixture units to flow rates. Section 606 covers the installation requirements for the water supply system. Section 608 covers backflow prevention.