Section 603.1/Water Supply System Design
UPC 603 covers water supply sizing using WSFU and pressure loss calculations specific to the Uniform Plumbing Code.
The water supply system must deliver water to all fixtures at the minimum flow rate and pressure required for proper operation. Pipe sizing is based on water supply fixture units (WSFU) assigned to each fixture type per Table 610.3. The total WSFU is converted to flow demand using Table 610.4. Pipe sizes are determined using the friction loss method, accounting for pipe length, fittings, elevation changes, water meter losses, and the available vs. required pressure.
Why this section exists
An undersized water supply system produces inadequate flow and pressure at fixtures, especially during peak demand. The UPC sizing method is similar in concept to the IPC method but uses different WSFU assignments and demand curves. In western US states that adopt the UPC, the designer must use the UPC tables rather than the IPC tables, as the fixture unit values and demand conversions differ.
What plan reviewers look for
Plan reviewers check the water supply calculation for total WSFU, peak demand flow rate, available street pressure, and pressure losses through the system. They verify pipe sizes on the plumbing plan match the calculation. They check the water meter and backflow preventer sizing. In jurisdictions that adopt the UPC, using IPC fixture unit values is a common error.
Common violations
Related UPC requirements
Section 701 covers drainage system sizing that uses a parallel but different fixture unit system. Table 610.3 provides UPC water supply fixture unit values. Table 610.4 converts WSFU to GPM demand. IPC Section 604 provides the equivalent requirements for IPC jurisdictions.