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 Fixtures||Minimum Fixture Branch Pipe Size||Water Supply Fixture Units|
|(inch)||Private Installations||Public Installations|
|Bathtub with 3/4" fill valve||3/4||10||10|
|Clinic fauce sink||1/2||3|
|Kitchen sink, domestic||1/2||1.5||1.5|
|Service or mop basin||1/2||1.5||3|
|Urinal with flush tank||1/2||2||2|
|Water closet with gravity tank||1/2||2.5||2.5|
|Water closet with flushometer tank||1/2||2.5||2.5|
- 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.