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Section 604 Design of Building Water Distribution System
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The design of the water distribution system shall conform to accepted engineering practice. Methods utilized to determine pipe sizes shall be approved.
At the points of interconnection between the hot and cold water supply piping systems and the individual fixtures, appliances or devices, provisions shall be made to prevent flow between such piping systems.
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.
| 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:
| 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.
| 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 street water main pressures fluctuate, the building water distribution system shall be designed for the minimum pressure available.
Wherever water pressure from the street main or other source of supply is insufficient to provide flow pressures at fixture outlets as required under Table 604.3, a water pressure booster system conforming to Section 606.5 shall be installed on the building water supply system.
The flow velocity of the water distribution system shall be controlled to reduce the possibility of water hammer. A water-hammer arrestor shall be installed where quick-closing valves are utilized. Water-hammer arrestors shall be installed in accordance with the manufacturer's instructions. Water-hammer arrestors shall conform to ASSE 1010.
Hot water and cold water manifolds installed with gridded or parallel connected individual distribution lines to each fixture or fixture fitting shall be designed in accordance with Sections 604.10.1 through 604.10.3.
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.
| 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.
Individual fixture shutoff valves installed at the manifold shall be identified as to the fixture being supplied.
Access shall be provided to manifolds with integral factory- or field-installed valves.
Where individual pressure balancing in-line valves for individual fixture fittings are installed, such valves shall comply with ASSE 1066. Such valves shall be installed in an accessible location and shall not be utilized alone as a substitute for the balanced pressure, thermostatic or combination shower valves required in Section 424.3.
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