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I have building with 16 showers , 6 toilets, 8 sinks and 6 urinals what size of water pipe should be for the supply?

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    Commercial or residential? How many people may be expected to be using these facilities simultaneously?
    – FreeMan
    Apr 28 '21 at 16:37
  • If all fixtures can be turned on at the same time then you need a 4 inch supply pipe. This assumes a half inch supply to each individual fixture. This would let you turn on all hot and cold lines at the same time.
    – MonkeyZeus
    Apr 28 '21 at 16:37
  • If you anticipate that only half of the fixtures will be in use at any given time then a 2.75 inch supply would be appropriate.
    – MonkeyZeus
    Apr 28 '21 at 16:38
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    @MonkeyZeus, you should be posting that as an answer and you should support it with reasoning or resources. Comments aren't the place for it.
    – isherwood
    Apr 28 '21 at 18:13
  • @isherwood Done, hopefully the math is understandable :)
    – MonkeyZeus
    Apr 28 '21 at 19:46
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In the U.S., water supply requirements are calculated using a table of water supply fixture units (wsfu) in the plumbing codes. Below, I use the values for a public/commercial installation (residential requirements are less but the OP's question appears to be a commercial setting):

fixture cold hot total
16 showers 48 48 64
6 toilets - flush valve 60 0 60
8 sinks 12 12 16
6 urinals - 1" flush valve 60 0 60
180 60 200

Notice the total values are not a sum of hot + cold; they are also from the WSFU table.

After determining all your WSFUs from all types of fixtures in the group, you need to know the minimum water pressure and maximum supply line length. These values, and the required WSFUs, allow you to consult a second table giving you the minimum supply pipe & meter size. In this case, a 2" supply should suffice.

This calculation should be performed for each branch of the plumbing system.

You should not invent your own method based on pipe diameter because the tables in the building codes already account for pressure drop due to length of the supply lines, and available supply pressure.

WSFU fixture requirements table WSFU supply table

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