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Water Supply vs. Fixture Water Requirements

Supply requirements for common fixtures.

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Each fixture in a water supply system represents a certain demand of water. Supply requirement for common fixtures:

FixtureFlow rateMinimum Supply Pressure
Aspirator 2.5 10 8 55
Bathtub faucet 5 19 8 55
Bidet 2 7.5 4 28
Combination fixture 4 15 8 55
Dish washing machine 4 15 8 55
Drinking fountain jet 0.75 3 8 55
Hose bib or sillcock, 1/2" 5 19 8 55
Laundry faucet 1/2" 5 19 8 55
Laundry machine 4 15 8 55
Lavatory faucet, ordinary 2 7.5 8 55
Lavatory faucet, self closing 2.5 10 8 55
Shower head 5 19 8 55
Shower, temperature controlled 3 10 20 138
Sink faucet 3/8", 1/2" 4.5 17 8 55
Sink faucet 3/4" 6 23 8 55
Urinal flush valve 15 56 15 110
Water closet with flush valve 35 132 25 170
Water closet with gravity tank 2.5 10 8 55
Water closet with close coupled tank, ballcock 3 11 8 55

Adding up the numbers to cover all fixtures in a system would give the total demand if all fixtures were used at the same time. This is  almost never realistic for a supply system. Reasonable estimates must be made based on simultaneously demand from the fixtures.

Water supply - expected demand vs. no. fixtures

Example - Required Water Supply

For a water supply system the summarized theoretical water flow for all fixtures is 10 l/s. The largest fixture in the system requires 0.4 l/s.

Based on the diagram above the expected total water flow in the system will be aprox. 1.1 l/s.

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  • Engineering ToolBox, (2004). Water Supply vs. Fixture Water Requirements. [online] Available at: [Accessed Day Mo. Year].

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