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Thread: Underwater supply pipe?

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    Questions from readers Guest's Avatar
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    Default Underwater supply pipe?

    I am contemplating a water supply pipe for four residential houses located on a cay where there is no water (except rain water caught in
    cisterns) and the nearest public water source is across a bay to one of two locations. The first is approximately 3/4 miles away and the other about 2 miles. The shorter one involves right of way issues, the longer, not. What kind of pipe can be used for this submerged installation and what diameter pipe should be considered adequate? I am trying to evaluate different scenarios and costs and am loathe to have an elaborate R.O. desal plant and all the requisite systems maintenance and expense associate to these systems...not the least of which is electricity to run the high pressure pumps (we have no power grid here but live totally solar with perfectly adequate results). Water is really the only significant obstacle here. It is possible that this supply need not be potable so different pipe materials may be appropriate for irrigation.
    Thanks, Hugh T
    Elizabeth Island, Exuma, Bahamas

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    In the Trades Wally Hays's Avatar
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    Let me get this straight. You want to run a 2 mile water main, underwater?
    Don't you need to get some sort of government permission to do this?

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    DIY Junior Member yellowdog's Avatar
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    There are issues galore with permitting, but the initial charge is to determine the best plan of attack and one step involves assembling a materials list for a pipe fed system from the municipal water company and yes, it could be as far as 2 miles. I am seeking information and prices of the appropriate sized pipe to serve the needs of four single family dwellings at a distance of 3/4 mile and 2 miles. I haven't been able to locate, but have heard of, hydraulic style hose piping available on spool or coiled that sinks and has a tendency to settle into the sea floor over time.
    Yelldog

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    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    2 miles long? You'd better be looking at some large piping to accomadate the flow rates and friction loss you'll suffer. I also would think you'd need booster pumps along the way to keep the pressures up.

    There is probably A LOT more involved in getting water to your house then you may think. It's not as simple as dropping a line in the water and getting it to give you water 2 miles away.

    Give me $225,000 and I'll fly to the bahamas and solve the problem for you. I accept pay-pal.

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    DIY Junior Member yellowdog's Avatar
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    Something told me this wasn't gonna be your basic garden hose variety! Maybe the 3/4 mile option(though thwarted with right of way problems) may be the only viable option. Thanks for the come back..YD

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    That's all folks! Gary Slusser's Avatar
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    Quote Originally Posted by Guest View Post
    I am contemplating a water supply pipe for four residential houses located on a cay where there is no water (except rain water caught in cisterns) and the nearest public water source is across a bay to one of two locations. The first is approximately 3/4 miles away and the other about 2 miles. The shorter one involves right of way issues, the longer, not.

    I am trying to evaluate different scenarios and costs and am loathe to have an elaborate R.O. desal plant and all the requisite systems maintenance and expense associate to these systems...not the least of which is electricity to run the high pressure pumps (we have no power grid here but live totally solar with perfectly adequate results). Water is really the only significant obstacle here. It is possible that this supply need not be potable
    The distance is a real problem but so are currents wanting the pipe somewhere else than where you want it to stay. For 4 houses, and 3/4s of a mile, maybe like 2.5 or 3" pipe.

    Which proves the theory that without water a house is worthless and yet may still cost you at least tax money. So it is usually a very good idea to provide for an adequate volume of usable water before building or buying real estate.

    What is it about the cistern and rain water that you are attempting to get away from?
    Gary Slusser Retired (= out of business)
    Click Here to learn how to correctly size or program a water softener.
    CAUTION, as of Nov 12 2013 all YouTube videos showing how to rebuild a Clack valve have an error in them that can cause damage.

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    Journeyman/Inspector Inspektor Ludwig's Avatar
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    hmm let's see,
    26 fixture units...
    at...48 psi...
    with head loss....at...uh huh...hold on....
    then water meter sized at...um ..hmm
    then length to furthest outlet.....and friciton loss....ok....hmm
    that would be....uh ok...hold on
    2 miles.......give or take 5 ft.
    so you'd need a ...hold on...(calculator key sounds)

    16" water service? Heck I may be off by a few inches. That's one heckova long roll of PE.

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    Moderator valveman's Avatar
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    I have a 1.5 mile line of 1.5" HDPE pipe to my house. At 5 GPM there is basically no friction loss. 5 GPM is 7200 gallons per day. Put that is a cistern and use a booster pump, and you could supply 20 houses.

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    DIY Junior Member yellowdog's Avatar
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    Quote Originally Posted by valveman View Post
    I have a 1.5 mile line of 1.5" HDPE pipe to my house. At 5 GPM there is basically no friction loss. 5 GPM is 7200 gallons per day. Put that is a cistern and use a booster pump, and you could supply 20 houses.
    Greetings Valveman, I was thinking of a scenario like that of which you speak. These houses are basic as they all run on a small solar array and share one auxiliary genset to punch up the batteries on occasion. The water useage is small, but we would love to be able to irrigate a bit of the land for various planting schemes. Your notion of smaller gpm and storage fits nicely. Because we will have all totaled about 70,000 gallons of cistern capacity, there is no shortage of places to put the water. That capacity is more than we expect to fill through a rainy season with the catchment surfaces we have, so augmenting it with that slow fill rate might do nicely.
    I gather your piping is not underwater, but on/or underground!?
    Thanks....Yellowdog

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    General Engineering Contractor ballvalve's Avatar
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    Quote Originally Posted by valveman View Post
    I have a 1.5 mile line of 1.5" HDPE pipe to my house. At 5 GPM there is basically no friction loss. 5 GPM is 7200 gallons per day. Put that is a cistern and use a booster pump, and you could supply 20 houses.
    I have a mile at 1.25" with the same scenario. Smaller pipe- low flow. Its hard to keep water pipe in position in the dirt, so I cant imagine the solution underwater. Take a look at how the trans ocean cables are built.

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