Anybody object to this pass/fail specification for city water delivery?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Thatguy, Oct 28, 2010.

  1. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    Based on [more or less] responses from two water utilities,
    an adequate city water supply for a single family house can deliver
    more than 5 GPM and
    between 20 & 80 PSI and
    PSI x GPM should be more than 400.

    This last line takes about 1/4 hp to accomplish and is my addition to this benchmark.
    Last edited: Oct 28, 2010
  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,825
    Location:
    Cave Creek, Arizona
    And WHAT is the relevence of PSI x GPM being 400? That does NOT create ANY useful measurement. IT is like a toilet's 1.6 gpf x 6 lpf equals approximately 10.
  3. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Why do you need to write a spec for the city? They will deliver what they feel like. Many places, they will deliver much higher than 80 psi, and rely on you to provide a regulator.

    The minimum gpm is based on meter size. A 1/2" or 5/8" meter will deliver 5 gpm. If you want more gpm, you have to PAY for a larger meter. And the city will deliver whatever volume you choose to pay for.
  4. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    Sorry for the misleading title.
    It's a spec for OPs to judge if their city water supply is substandard or if a pipe is partially clogged. That question/complaint comes up a lot.

    The static pressure and max flow rate is not hard to get, but the 400 is an approximation to a pump curve between these two endpoints. It corresponds to about a 1/4 to 1/2 hp pump.

    If your house can maintain 40 PSI while delivering 16 GPM you're doing well. 5 GPM @ 5 PSI is terrible.

    Here's what two WaCos said

    Per the Department of Health Waterworks Regulations the
    minimum allowable delivery pressure is 20 psi.
    . . .our targeted range for delivery pressure is 40 to 80 psi. Flow rates are a function
    of demand but a standard size residential meter (5/8") has a maximum
    capacity of about 20 gpm.

    and

    We don't use a benchmark. The pressure range is between 40 and 80lbs. if
    below 40 a booster pump is need and above 80 a pressure reducing valve.
    Last edited: Oct 28, 2010
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,825
    Location:
    Cave Creek, Arizona
    The usual calculation is gpm AT a specific psi, NOT gpm TIMES psi, (which does not yield any kind of useful number).
  6. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    GPM at a specific PSI or feet of head implies horsepower.
    hp = (head x GPM)/3956 for water.

    If you wanted to simulate city water and you lived next to a lake and your house was a few inches above the lake's surface, a 1/2 hp pump at any depth would probably work.

    I think the WaCos don't use this because almost always just a static pressure and working water meter guarantees a usable water supply. Only when there is a problem do they use instruments and charts.
    Last edited: Oct 29, 2010
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