According to Ignoramus22745 :

I am thinking, if I record pressure, low pressure when all faucets are
closed means a city water problem. If not, low pressure when one
faucet is open means a house problem. Is that right?

Not quite.

In short, you're trying to distinguish between having a pressure problem
and a flow rate problem.

If you have low pressure when all faucets are closed, it's a low pressure
problem and the city's issue - _unless_ it's a defective pressure regulator
(if you have one).

Once you've eliminated low pressure as the issue, trying to interpret
pressure levels and thereby implicitly figure out flow rate problems doesn't
necessarily tell you where the problem is. It could be anywhere up to and
including the supply line into your house from the street.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.