Water Supply Fixture Units - WSFU

WSFU is used to calculate water supply service systems

The WFSU (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:

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  
Dishwasher, domestic 1/2 1.5 1.5
Drinking fountain 1/2 0.5 0.5
Hose Bibb 1/2 2.5 2.5
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
Washup basin 1/2 2  
Shower head 1/2 2 2
Urinal with flush tank 1/2 2 2
Wash fountain 3/4 4  
Water closet with gravity tank 1/2 2.5 2.5
Water closet with flushometer tank 1/2 2.5 2.5
Water cooler 1/2 0.5 0.5
  • 1 WSFU = 1 GPM = 3.79 liter/min

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 - Hot and cold water service systems - design properties, capacities, sizing and more

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