On 2010-08-10, The Post Quartermaster
wrote:

I'm going to run a water line out to a little outbuilding I have out
near the barn. The line I am going to tap off of is probably a 3/4"
line. If I run a larger diameter, say a 1 or 11/4 inch from there to
the outbuilding would that result in any increase in pressure at the
outbuilding or would the fact that there was a 3/4" feed negate any
increase?

The way to approach this question is what are the water uses you will
have in the outbuilding and what flow rates do they demand? If you
just have a lavatory, it only needs 1.5 gpm, and since you said it is
only 40', the 3/4" pipe will be fine, and you'll never see the
difference if you upsize to 1" pipe. But if you want to fill a
bathtub as quickly as possible, then yes, the 1" pipe will give you
more flow.

Cheers, Wayne