Ignoramus22745 wrote:
I am trying to wrap up a few issues with the house.

We have a relatively nice house (ie not terribly cheaply built, 25 yrs
old), but we have a strange problem that has become bad lately. It is
either low water pressure or low water flow. Some facts

- If I am taking a shower and someone turns on some water faucet, even
not too much, the flow drops dramatically

- It applies to both hot and cold water

SNIP

Ask neighbors if they have same problem.
As suggested, get the softener out of the circuit.
If there is a "Bypass" arrangement, make sure it is Open.

Your 30psi gauge may go off scale, but a gauge set up
the way you describe is a good test.

Any chance the supply piping in the house is galv iron?

Is there a pressure reducing valve on the water service?

Jim