We are in the process of designing and planning a new home. The location is relatively rural, but there is a water supply to the street. In order to tap the supply, I have my choice of three options - 5/8" for $5K, 3/4" for $7.5K, or 1" for $10K.

Ultimately, this home will be approximately 5000 sq ft with up to 7 bedrooms and two complete living areas (2 Kitchens, 2 laundries, 5 or more bathrooms - you get the idea (two houses under one roof). I'm worried that even a 1" source will not be an adequate, if more than two taps get opened at one time.

I had the thought of going with the 5/8" source, but feeding a large capacity tank (2500 gallons). Then using a booster pump to feed both homes with larger lines. Then I can control the volume and pressure and the 5/8 source can "back-fill" the holding tank as needed.

I'm no master plumber... Just trying to come-up with a plan to best suit my long term needs. Any thoughts on this? Thanks.

not so simple to answer without more info..
how big is the main on the street?
what is the pressure at the street?
how far from the street to the house?
can you tap 1 1/4"?

Figuring the cost of the holing tanks and pumps plus the cost of repairs and replacements , I would opt for a 1" tap and not be bothered with the other items.

Other background details requested:


how big is the main on the street?

I don't know the exact size of the main at the street, but it feeds other homes in the subdivision (all lots are 5 acres or more) as well as fire hydrants along the road. We are at a mid-point, not the end.

what is the pressure at the street?

Unknown at this time. I talked with a neighbor. He said they have never had pressure issues, but the volume visibly changes when multiple taps are actuated. However, he also couldn't tell me which size tap they have.

how far from the street to the house?

The setback restrictions require at least 150' from the street. More than likely we are not going to build at the setback edge of the lot either... so probably several hundred feet (350 to 400)

can you tap 1 1/4"?

I've heard they may be able to provide larger taps, but I suspect the pricing skyrockets from the 1" price. They come and give you a site evaluation and custom engineering to determine the estimate (you pay something like $1500 just for the estimate).

A 1" METER and supply pipe to it will be more than adequate. YOUR pipe from the meter to the building, however can be larger. The "small pipe into a holding tank" is ONLY used when the water supply is inadequate or irregular, but is a poor substitute for an adequately sized supply system.

"what is the pressure at the street? = Unknown at this time"

Unless we know the exact lowest pressure that the main supply might have at any time of a day we can't give you a really good definitive answer as to what will be an adequate minimum size pipe.

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"how far from the street to the house? = ...probably several hundred feet (350 to 400)"

Without knowing the pressure I would say go with as large of pipe as you can afford.

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"....neighbor. He said they have never had pressure issues, but the volume visibly changes when multiple taps are actuated.

My alarms are going off ...... your neighbor hasn't given you enough info.

Best to get a "lazy hand" water pressure gauge [www.plumbingsupply.com]
and attach it to your neighbors hosebibb for a few days (I'm assuming you're on flat land, if not add/subtract .43 lbs per foot of height compared to your neighbor).

If you're planning on building a 5000 sq ft home with 2 kitchens, 2 laundries, 5 or more bathrooms you are going to have to know the exact pressure to get exact sizing.

If you can avoid a booster pump, tank, etc in the long run you will be much happier.

tap for and install a 1" meter

run 1.25" from meter to home to avoid loss from long run pressure drop

make sure internal piping is done correctly

probably 3/4 or 1" 'mains' with individual fixture branches of 1/2"

or, if PEX,

manifold and 'home run' to each fixture

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

one thing you need to know about sizing a water main....
the smaller the pipe is, more of the water traveling thru the pipe rubs against the sides of the pipe slowing it down. (friction)
in a larger pipe there is less friction per gallon of water delivered.
so, this is a great question that may very well take an engineer to answer.

1 1/4" being a "bast_rd size", most plumbers would opt for 1 1/2".



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Will this water also be used to supply a fire suppression system?

Thanks for all the feedback. At this time, a fire suppression system was not planned as part of the design.



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