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Water Supply Lines - Sizing

Sizing water supply service and distribution lines based on Water Supply Fixture Units (WSFU).

Due to intermittent use of the fixtures in a water supply system it can be difficult to predict and size the supply and service lines. The fixtures total theoretical demand should always be compensated with a statistic more expected demand.

With the Water Supply Fixture Units (WSFU) system defined by the Uniform Plumbing Code (UPC) there are tables available where the total demand calculated by adding each units "Water Supply Fixture Units" (WFSU) are compensated to an expected demand.

The tables below can be used to size building supply and branch lines and meter and service lines.

Supply pressure 30 - 45 psi

Water Supply Lines - Sizing - Supply pressure 30 - 45 psi
Meter and street service lines
(inches)
Building supply and branch lines
(inches)
Maximum Water Supply Fixture Units (WSFU)
Length of pipe (feet)
406080100150200
3/4 1/2 6 5 4 3 2 1
3/4 19 16 14 12 9 6
1 29 25 23 21 17 15
1 1 36 31 27 25 20 17
1 1/4 54 47 42 38 32 28

WSFU - Fixture Units -  Maximum Water Supply

Supply pressure 45 - 60 psi

Water Supply Lines - Sizing - Supply pressure 45 - 60 psi
Meter and street service lines
(inches)
Building supply and branch lines
(inches)
Maximum Water Supply Fixture Units (WSFU)
Length of pipe (feet)
406080100150200
3/4 1/2 7 7 6 5 4 3
3/4 20 20 19 17 14 11
1 39 39 36 33 28 23
1 1 39 39 39 36 30 25
1 1/4 78 78 76 67 52 44

Supply pressure over 60 psi

Water Supply Lines - Sizing - Supply pressure  > 60 psi
Meter and street service lines
(inches)
Building supply and branch lines
(inches)
Maximum Water Supply Fixture Units (WSFU)
Length of pipe (feet)
406080100150200
3/4 1/2 7 7 7 6 5 4
3/4 20 20 20 20 17 13
1 39 39 39 39 35 30
1 1 39 39 39 39 38 32
1 1/4 78 78 78 78 74 62
  • 1 in = 25.4 mm

The tables can be used for pipe lines but for special equipment like manifolds etc. a table or formula converting the WSFU to water flow should be used for proper sizing.  

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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