My house is on a shared lot, and the water supply comes from a pipe supplied near the main house. We're not quite sure how everything is connected there, but from measuring pressure drops, we do know that there's (approximately) 100ft of 1/2" copper pipe leading to the supply at my house and that typically I see a 9psi drop (from 65psi) when running a showerhead (2.5gpm).
We also tested how my pressure varies when the main house is running water. I get extreme pressure drops when they activate a tub faucet. It goes from 65 to 49psi. I also typically get drops of around 5-10 psi when they turn on one or two showerheads (2.5 or 5gpm).
We're going to be redoing the plumbing in my place with descending lines from the attic since we have no real crawlspace access. I was wondering if there is a way to use a small holding tank (in the attic, around 4m above the supply entry) to buffer the water pressure so I don't experience quite as severe pressure losses when the main house runs water.
Best Answer
Pressure drops are normal. That's just how it works. Even with much larger pipe, there'll be pressure changes as the pump kicks in and out.
I would start with a pressure regulator. Set the regulator for something like 35 PSI which the system can always provide. It would work even better if both houses had a pressure regulator. It goes without saying that this will reduce best-condition flow somewhat, in favor of more uniform flow all the time.
After you have a regulator (which implies a check valve), then a "pressure tank" will start to make sense. This buffers further. Although I have a concern with them in light of what we're learning about hot water heaters and legionella. If it's not good for water to be stagnant in a hot water heater below 140F, one of those pressure tanks has the same basic problem.