Section 604 Design of Building Water Distribution System
The water distribution system shall be designed, and pipe sizes shall be selected such that under conditions of peak demand, the capacities at the fixture supply pipe outlets shall be not less than shown in Table 604.3. The minimum flow rate and flow pressure provided to fixtures and appliances not listed in Table 604.3 shall be in accordance with the manufacturer's installation instructions.
WATER DISTRIBUTION SYSTEM DESIGN CRITERIA REQUIRED CAPACITY AT FIXTURE SUPPLY PIPE OUTLETS
| FIXTURE SUPPLY OUTLET SERVING | FLOW RATEa (gpm) | FLOW PRESSURE (psi) |
| Bathtub, balanced-pressure, thermostatic or combination balanced-pressure/thermostatic mixing valve | 4 | 20 |
| Bidet, thermostatic mixing valve | 2 | 20 |
| Combination fixture | 4 | 8 |
| Dishwasher, residential | 2.75 | 8 |
| Drinking fountain | 0.75 | 8 |
| Laundry tray | 4 | 8 |
| Lavatory, private | 0.8 | 8 |
| Lavatory, private, mixing valve | 0.8 | 8 |
| Lavatory, public | 0.4 | 8 |
| Shower | 2.5 | 8 |
| Shower, balanced-pressure, thermostatic or combination balanced-pressure/thermostatic mixing valve | 2.5b | 20 |
| Sillcock, hose bibb | 5 | 8 |
| Sink, residential | 1.75 | 8 |
| Sink, service | 3 | 8 |
| Urinal, valve | 12 | 25 |
| Water closet, blow out, flushometer valve | 25 | 45 |
| Water closet, flushometer tank | 1.6 | 20 |
| Water closet, siphonic, flushometer valve | 25 | 35 |
| Water closet, tank, close coupled | 3 | 20 |
| Water closet, tank, one piece | 6 | 20 |
For SI: 1 pound per square inch = 6.895 kPa, 1 gallon per minute = 3.785 L/m.
- For additional requirements for flow rates and quantities, see Section 604.4.
- Where the shower mixing valve manufacturer indicates a lower flow rating for the mixing valve, the lower value shall be applied.
The maximum water consumption flow rates and quantities for all plumbing fixtures and fixture fittings shall be in accordance with Table 604.4.
Exceptions:
- Blowout design water closets having a water consumption not greater than 31/2 gallons (13 L) per flushing cycle.
- Vegetable sprays.
- Clinical sinks having a water consumption not greater than 41/2 gallons (17 L) per flushing cycle.
- Service sinks.
- Emergency showers.
MAXIMUM FLOW RATES AND CONSUMPTION FOR PLUMBING FIXTURES AND FIXTURE FITTINGS
| PLUMBING FIXTURE OR FIXTURE FITTING | MAXIMUM FLOW RATE OR QUANTITYb |
| Lavatory, private | 2.2 gpm at 60 psi |
| Lavatory, public (metering) | 0.25 gallon per metering cycle |
| Lavatory, public (other than metering) | 0.5 gpm at 60 psi |
| Shower heada | 2.5 gpm at 80 psi |
| Sink faucet | 2.2 gpm at 60 psi |
| Urinal | 1.0 gallon per flushing cycle |
| Water closet | 1.6 gallons per flushing cycle |
For SI: 1 gallon = 3.785 L, 1 gallon per minute = 3.785 L/m, 1 pound per square inch = 6.895 kPa.
- A hand-held shower spray is a shower head.
- Consumption tolerances shall be determined from referenced standards.
The minimum size of a fixture supply pipe shall be as shown in Table 604.5. The fixture supply pipe shall terminate not more than 30 inches (762 mm) from the point of connection to the fixture. A reduced-size flexible water connector installed between the supply pipe and the fixture shall be of an approved type. The supply pipe shall extend to the floor or wall adjacent to the fixture. The minimum size of individual distribution lines utilized in gridded or parallel water distribution systems shall be as shown in Table 604.5.
MINIMUM SIZES OF FIXTURE WATER SUPPLY PIPES
| FIXTURE | MINIMUM PIPE SIZE (inch) |
| Bathtubsa (60" × 32" and smaller) | 1/2 |
| Bathtubsa (larger than 60" × 32") | 1/2 |
| Bidet | 3/8 |
| Combination sink and tray | 1/2 |
| Dishwasher, domestica | 1/2 |
| Drinking fountain | 3/8 |
| Hose bibbs | 1/2 |
| Kitchen sinka | 1/2 |
| Laundry, 1, 2 or 3 compartmentsa | 1/2 |
| Lavatory | 3/8 |
| Shower, single heada | 1/2 |
| Sinks, flushing rim | 3/4 |
| Sinks, service | 1/2 |
| Urinal, flush tank | 1/2 |
| Urinal, flushometer valve | 3/4 |
| Wall hydrant | 1/2 |
| Water closet, flush tank | 3/8 |
| Water closet, flushometer tank | 3/8 |
| Water closet, flushometer valve | 1 |
| Water closet, one piecea | 1/2 |
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square inch = 6.895 kPa.
- Where the developed length of the distribution line is 50 feet or less, and the available pressure at the meter is 35 psi or greater, the minimum size of an individual distribution line supplied from a manifold and installed as part of a parallel water distribution system shall be one nominal tube size smaller than the sizes indicated.
Where water pressure within a building exceeds 80 psi (552 kPa) static, an approved water pressure-reducing valve conforming to ASSE 1003 or CSA B356 with strainer shall be installed to reduce the pressure in the building water distribution piping to not greater than 80 psi (552 kPa) static.
Exception: Service lines to sill cocks and outside hydrants, and main supply risers where pressure from the mains is reduced to 80 psi (552 kPa) or less at individual fixtures.
Hot water and cold water manifolds shall be sized in accordance with Table 604.10.1. The total gallons per minute is the demand of all outlets supplied.
MANIFOLD SIZING
| NOMINAL SIZE INTERNAL DIAMETER (inches) | MAXIMUM DEMAND (gpm) | |
| Velocity at 4 feet per second | Velocity at 8 feet per second | |
| 1/2 | 2 | 5 |
| 3/4 | 6 | 11 |
| 1 | 10 | 20 |
| 11/4 | 15 | 31 |
| 11/2 | 22 | 44 |
For SI: 1 inch = 25.4 mm, 1 gallon per minute = 3.785 L/m, 1 foot per second = 0.305 m/s.