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Water Supply Fixture Units (WSFU) for Different Fixtures with Minimum Pipe Sizes

Er. Parbhakar Dwivedi


The rates at which water is desirably drawn into different types of fixtures are known. These rate become whole numbers of small size when they are expressed in fixture unit. The water supply fixture units (WSFU) for different sanitary appliances or groups of appliances are given

S. No. Type of Fixture Application Private Application Public Minimum Pipe Size mm
1 Bathtub 1 - 15
2 Ablution faucet/Bidet 1 1 15
3 Clothes washer 1 4 (see note 7) 15
4 Dishwasher 1.5 1.5 15
5 Drinking fountain - 0.5 (0.75) 15
6 Hose bib 2.5 2.5 15
7 Wash basin (with metered faucet) 1 1 15
8 Wash basin (with standard faucet) 1.5 1.5 (2) 15
9 Service sink 1.5 3 15
10 Kitchen sink 2 4 15
11 Surgical sink - 2 15
12 Scrub station in hospital (per outlet) - 3 15
13 Scrub station in hospital (per outlet) 2 3 15
14 Bathroom group (flush tank) 5 6 20
15 Bathroom group (flush valve) 8 10 25 / 32
16 Urinal (flush valve) 3 5 (6) 20
17 Urinal (flush tank) 2 2 (3) 15
18 Urinal (sensor operated) 2 2 (3) 15
19 Water closet (flush valve) 6 8 (10) 25 / 32
20 Water closet (flush tank) 2 3 (5) 15
21 Combination fixture (faucet) 3 - 15
22 Laundry trays (faucet) 3 - 15


1 The above table is based on Hunter’s method.

2 Hunter’s method of estimating load in plumbing systems is based on assigning a fixture unit (FU) weight to the plumbing fixtures and then converting these to equivalent litre per minute, based on the theory of probability of usage and based on the observation that all fixtures are not used simultaneously.

3 The fixture unit concept is a method of calculating maximum probable water demand within large buildings based on theory of probability. The method is based on assigning a fixture unit (FU) value to each type of fixture based on its rate of water consumption, on the length of time it is normally in use and on the average period between successive uses.

4 The values of probable demand will not change in respect of systems with flush valves and flush tanks for fixture units more than 1 000.

5 The fixtures or appliances which are not included in the above table may be sized referring to fixtures having similar flow rate and frequency of usage.

6 The minimum supply branch pipe sizes for individual fixtures are nominal sizes.

7 The clothes washer for public does not include large washer extractors, and in such cases the pipe sizing shall be determined as per manufacturer’s recommendations.

8 For more information on bathroom groups, reference may be made to specialist literature

9 The fixture units listed in the above table represent the load for cold water service. The separate cold and hot water fixture unit value for fixtures having both hot and cold water connections may each be taken as three quarter of the listed total value of fixture.

10 A shower head over a bath tub does not increase the fixture unit value.

11 The values given in parentheses pertain to such public use buildings (congregation halls) where an enhanced requirement is expected to be encountered as compared to the normal maximum use in public use buildings


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