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Water Supply Fixture Units WSFU

WSFU is used to calculate water supply service systems.

The WSFU (Water Supply Fixture Units) is defined by the Uniform Plumbing Code (UPC) and can be used to determine water supply to fixtures and their service systems.

Water Supply vs. Fixture Units
Individual FixturesMinimum Fixture Branch Pipe SizeWater Supply Fixture Units
WSFU
(inch)Private InstallationsPublic Installations
Bathtub 1/2 4 4
Bathtub with 3/4" fill valve 3/4 10 10
Bidet 1/2 1  
Combination sink and tray 1/2
Dishwasher, domestic 1/2 1.5 1.5
Drinking fountain 1/2 0.5 0.5
Hose bibbs 1/2 2.5 2.5
Laundry, 1 - 3 compartments 1/2
Lavatory 1/2 1 1
Bar sink 1/2 1 2
Clinic fauce sink 1/2 3  
Kitchen sink, domestic 1/2 1.5 1.5
Laundry sink 1/2 1.5 1.5
Service or mop basin 1/2 1.5 3
Sinks, flushing rim 3/4
Sinks, service 1/2
Washup basin 1/2 2  
Shower, single head 1/2 2 2
Urinal, flush tank 1/2 2 2
Urinal, flushometer valve 3/4
Wall hydrant 1/2
Wash fountain 3/4 4  
Water closet, gravity flush tank 1/2 2.5 2.5
Water closet, flushometer valve 1 2.5 2.5
Water cooler 1/2 0.5 0.5
  • 1 WSFU = 1 GPM = 3.79 liter/min
  • 1 in = 25.4 mm

Note that this conversion is only true for one or a few fixtures. Since all fixtures in a system are never used at the same time, the total units achieved by adding the numbers for all fixtures must be compensated for their intermittent use.

For supply pipe lines this is taken care of in the sizing tables.  

For manifolds or special equipments sizing, a formula or a table can be used.

Related Topics

  • Water Systems

    Design of hot and cold water service and utility systems with properties, capacities, sizing of pipe lines and more.

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