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P2903.1 Water Supply System Design Criteria
The water service and water distribution systems shall be designed and sized for peak demand using values shown in Table P2903.1.
TABLE P2903.1
REQUIRED CAPACITIES AT POINT OF OUTLET DISCHARGE
FIXTURE SUPPLY OUTLET SERVING FLOW RATE (gpm) FLOW PRESSURE (psi)
Bathtub, balanced-pressure, thermostatic or combination balanced-pressure/thermostatic mixing valve 4 20
Bidet, thermostatic mixing valve 2 20
Dishwasher 2.75 8
Laundry tray 4 8
Lavatory 0.8 8
Shower, balanced-pressure, thermostatic or combination balanced-pressure/thermostatic mixing valve 2.5a 20
Sillcock, hose bibb 5 8
Sink 1.75 8
Water closet, flushometer tank 1.6 20
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.
  1. Where the shower mixing valve manufacturer indicates a lower flow rating for the mixing valve, the lower value shall be applied.
P2903.2 Maximum Flow and Water Consumption
The maximum water consumption flow rates and quantities for plumbing fixtures and fixture fittings shall be in accordance with Table P2903.2.
TABLE P2903.2
MAXIMUM FLOW RATES AND CONSUMPTION FOR PLUMBING FIXTURES AND FIXTURE FITTINGSb
PLUMBING FIXTURE OR FIXTURE FITTING MAXIMUM FLOW RATE OR QUANTITY
Lavatory faucet 2.2 gpm at 60 psi
Shower heada 2.5 gpm at 80 psi
Sink faucet 2.2 gpm at 60 psi
Water closet 1.6 gallons per flushing cycle
For SI: 1 gallon per minute = 3.785 L/m, 1 pound per square inch = 6.895 kPa.
  1. A hand-held shower spray shall be considered to be a shower head.
  2. Consumption tolerances shall be determined from referenced standards.
P2903.3 Minimum Pressure
Where the water pressure supplied by the public water main or an individual water supply system is insufficient to provide for the minimum pressures and quantities for the plumbing fixtures in the building, the pressure shall be increased by means of an elevated water tank, a hydropneumatic pressure booster system or a water pressure booster pump.
P2903.3.1 Pumps Handling Drinking Water
Pumps intended to supply drinking water shall conform to NSF 61.
P2903.3.2 Maximum Pressure
The static water pressure shall be not greater than 80 psi (551 kPa). Where the main pressure exceeds 80 psi (551 kPa), an approved pressure-reducing valve conforming to ASSE 1003 or CSA B356 shall be installed on the domestic water branch main or riser at the connection to the water service pipe.
P2903.4 Thermal Expansion Control
A means for controlling increased pressure caused by thermal expansion shall be installed where required in accordance with Sections P2903.4.1 and P2903.4.2.
P2903.4.1 Pressure-Reducing Valve
For water service system sizes up to and including 2 inches (51 mm), a device for controlling pressure shall be installed where, because of thermal expansion, the pressure on the downstream side of a pressure-reducing valve exceeds the pressure-reducing valve setting.
P2903.4.2 Backflow Prevention Device or Check Valve
Where a backflow prevention device, check valve or other device is installed on a water supply system using storage water heating equipment such that thermal expansion causes an increase in pressure, a device for controlling pressure shall be installed.
P2903.5 Water Hammer
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.
P2903.6 Determining Water Supply Fixture Units
Supply loads in the building water distribution system shall be determined by total load on the pipe being sized, in terms of water supply fixture units (w.s.f.u.), as shown in Table P2903.6, and gallon per minute (gpm) flow rates [see Table P2903.6(1)]. For fixtures not listed, choose a w.s.f.u. value of a fixture with similar flow characteristics.
TABLE P2903.6
WATER SUPPLY FIXTURE UNIT VALUES FOR VARIOUS PLUMBING FIXTURES AND FIXTURE GROUPS
TYPE OF FIXTURES OR GROUP OF FIXTURES WATER-SUPPLY FIXTURE-UNIT VALUE (w.s.f.u.)
Hot Cold Combined
Bathtub (with/without overhead shower head) 1.0 1.0 1.4
Clothes washer 1.0 1.0 1.4
Dishwasher 1.4 1.4
Full-bath group with bathtub (with/without shower head) or shower stall 1.5 2.7 3.6
Half-bath group (water closet and lavatory) 0.5 2.5 2.6
Hose bibb (sillcock)a 2.5 2.5
Kitchen group (dishwasher and sink with or without food-waste disposer) 1.9 1.0 2.5
Kitchen sink 1.0 1.0 1.4
Laundry group (clothes washer standpipe and laundry tub) 1.8 1.8 2.5
Laundry tub 1.0 1.0 1.4
Lavatory 0.5 0.5 0.7
Shower stall 1.0 1.0 1.4
Water closet (tank type) 2.2 2.2
For SI: 1 gallon per minute = 3.785 L/m.
  1. The fixture-unit value 2.5 assumes a flow demand of 2.5 gallons per minute, such as for an individual lawn sprinkler device. If a hose bibb or sill cock will be required to furnish a greater flow, the equivalent fixture-unit value may be obtained from this table or Table P2903.6(1).
CONVERSIONS FROM WATER SUPPLY FIXTURE UNIT TO GALLON PER MINUTE FLOW RATES
SUPPLY SYSTEMS PREDOMINANTLY FOR FLUSH TANKS SUPPLY SYSTEMS PREDOMINANTLY FOR FLUSHOMETER VALVES
Load Demand Load Demand
(Water supply fixture units) (Gallons per minute) (Cubic feet per minute) (Water supply fixture units) (Gallons per minute) (Cubic feet per minute)
1 3.0 0.04104
2 5.0 0.0684
3 6.5 0.86892
4 8.0 1.06944
5 9.4 1.256592 5 15.0 2.0052
6 10.7 1.430376 6 17.4 2.326032
7 11.8 1.577424 7 19.8 2.646364
8 12.8 1.711104 8 22.2 2.967696
9 13.7 1.831416 9 24.6 3.288528
10 14.6 1.951728 10 27.0 3.60936
11 15.4 2.058672 11 27.8 3.716304
12 16.0 2.13888 12 28.6 3.823248
13 16.5 2.20572 13 29.4 3.930192
14 17.0 2.27256 14 30.2 4.037136
15 17.5 2.3394 15 31.0 4.14408
16 18.0 2.90624 16 31.8 4.241024
17 18.4 2.459712 17 32.6 4.357968
18 18.8 2.513184 18 33.4 4.464912
19 19.2 2.566656 19 34.2 4.571856
20 19.6 2.620128 20 35.0 4.6788
25 21.5 2.87412 25 38.0 5.07984
30 23.3 3.114744 30 42.0 5.61356
35 24.9 3.328632 35 44.0 5.88192
40 26.3 3.515784 40 46.0 6.14928
45 27.7 3.702936 45 48.0 6.41664
50 29.1 3.890088 50 50.0 6.684
For SI: 1 gallon per minute = 3.785 L/m, 1 cubic foot per minute = 0.4719 L/s.
P2903.7 Size of Water-Service Mains, Branch Mains and Risers
The size of the water service pipe shall be not less than 3/4 inch (19 mm) diameter. The size of water service mains, branch mains and risers shall be determined from the water supply demand [gpm (L/m)], available water pressure [psi (kPa)] and friction loss caused by the water meter and developed length of pipe [feet (m)], including equivalent length of fittings. The size of each water distribution system shall be determined according to design methods conforming to acceptable engineering practice, such as those methods in Appendix AP and shall be approved by the building official.
P2903.8 Gridded and Parallel Water Distribution Systems
Hot water and cold water manifolds installed with parallel-connected individual distribution lines and cold water manifolds installed with gridded distribution lines to each fixture or fixture fitting shall be designed in accordance with Sections P2903.8.1 through P2903.8.5. Gridded systems for hot water distribution systems shall be prohibited.
P2903.8.1 Sizing of Manifolds
Manifolds shall be sized in accordance with Table P2903.8.1. Total gallons per minute is the demand for all outlets.
TABLE P2903.8.1
MANIFOLD SIZINGa
PLASTIC METALLIC
Nominal Size ID (inches) Maximumb gpm Nominal Size ID (inches) Maximumb gpm
3/4 17 3/4 11
1 29 1 20
11/4 46 11/4 31
11/2 66 11/2 44
For SI: 1 inch = 25.4 mm, 1 gallon per minute = 3.785 L/m, 1 foot per second = 0.3048 m/s.
  1. See Table P2903.6 for w.s.f.u and Table P2903.6(1) for gallon-per-minute (gpm) flow rates.
  2. Based on velocity limitation: plastic, 12 feet per second; metal, 8 feet per second.
P2903.8.2 Minimum Size
Where the developed length of the distribution line is 60 feet (18 288 mm) or less, and the available pressure at the meter is not less than 40 pounds per square inch (276 kPa), the size of individual distribution lines shall be not less than 3/8 inch (10 mm) diameter. Certain fixtures such as one-piece water closets and whirlpool bathtubs shall require a larger size where specified by the manufacturer. Where a water heater is fed from the end of a cold water manifold, the manifold shall be one size larger than the water heater feed.
P2903.8.3 Support and Protection
Plastic piping bundles shall be secured in accordance with the manufacturer's instructions and supported in accordance with Section P2605. Bundles that have a change in direction equal to or greater than 45 degrees (0.79 rad) shall be protected from chafing at the point of contact with framing members by sleeving or wrapping.
P2903.8.4 Valving
Fixture valves, when installed, shall be located either at the fixture or at the manifold. Valves installed at the manifold shall be labeled indicating the fixture served.
P2903.8.5 Hose Bibb Bleed
A readily accessible air bleed shall be installed in hose bibb supplies at the manifold or at the hose bibb exit point.
P2903.9 Valves
Valves shall be installed in accordance with Sections P2903.9.1 through P2903.9.5.
P2903.9.1 Service Valve
Each dwelling unit shall be provided with an accessible main shutoff valve near the entrance of the water service. The valve shall be of a full-open type having nominal restriction to flow, with provision for drainage such as a bleed orifice or installation of a separate drain valve. Additionally, the water service shall be valved at the curb or lot line in accordance with local requirements.
P2903.9.2 Water Heater Valve
A readily accessible full-open valve shall be installed in the cold-water supply pipe to each water heater at or near the water heater.
P2903.9.3 Fixture Valves and Access
Shutoff valves shall be required on each fixture supply pipe to each plumbing appliance and to each plumbing fixture other than bathtubs and showers. Valves serving individual plumbing fixtures, plumbing appliances, risers and branches shall be accessible.
P2903.9.4 Valve Requirements
Valves shall be compatible with the type of piping material installed in the system. Valves shall conform to one of the standards indicated in Table P2903.9.4 or shall be approved. Valves intended to supply drinking water shall meet the requirements of NSF 61.
TABLE P2903.9.4
VALVES
MATERIAL STANDARD
Chlorinated polyvinyl chloride (CPVC) plastic ASME A112.4.14, ASME A112.18.1/CSA B125.1, ASTM F1970, CSA B125.3, MSS SP-122
Copper or copper alloy ASME A112.4.14, ASME A112.18.1/CSA B125.1, ASME B16.34, CSA B125.3, MSS SP-67, MSS SP-80, MSS SP-110, MSS SP-139
Gray and ductile iron ASTM A126, AWWA C500, AWWA C504, AWWA C507, MSS SP-42, MSS SP-67, MSS SP-70, MSS SP-71, MSS SP-72, MSS SP-78
Cross-linked polyethylene (PEX) plastic ASME A112.4.14, ASME A112.18.1/CSA B125.1, CSA B125.3, NSF 359
Polypropylene (PP) plastic ASME A112.4.14, ASTM F2389
Polyvinyl chloride (PVC) plastic ASME A112.4.14, ASTM F1970, MSS SP-122
P2903.9.5 Valves and Outlets Prohibited Below Grade
Potable water outlets and combination stop-and-waste valves shall not be installed underground or below grade. Freezeproof yard hydrants that drain the riser into the ground are considered to be stop-and-waste valves.
Exception: Installation of freezeproof yard hydrants that drain the riser into the ground shall be permitted if the potable water supply to such hydrants is protected upstream of the hydrants in accordance with Section P2902 and the hydrants are permanently identified as nonpotable outlets by approved signage that reads, "CAUTION, NONPOTABLE WATER. DO NOT DRINK."
P2903.10 Hose Bibb
Hose bibbs subject to freezing, including the "frostproof" type, shall be equipped with an accessible stop-and-waste-type valve inside the building so that they can be controlled and drained during cold periods.
Exception: Frostproof hose bibbs installed such that the stem extends through the building insulation into an open heated or semiconditioned space need not be separately valved (see Figure P2903.10).

FIGURE P2903.10
TYPICAL FROSTPROOF HOSE BIBB INSTALLATION NOT REQUIRING SEPARATE VALVE
P2903.11 Drain Water Heat Recovery Units
Drain water heat recovery units shall be in accordance with Section N1103.5.3.

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