My mom lives in an old, two-story home (plus basement) in the city of Detroit. For the last 20 years, the upstairs shower has had low water pressure.
The shower consists of a ceramic tiled surround with plaster upper wall and cieling. The shower butts up against the tub (also with a tile surround).
I see no signs of leakage in the surrounds, upper walls or floors. The water coming from the shower is just the puniest thing. The sink and tub produce enough water to avoid concern. All of the plumbing leading from the lower story is behind a plaster wall in the stairwell (which shows no sign of leakage). I mentioned this house is in the city, as an indication that perhaps it gets sufficient pressure from the city.
What steps can I take to get the pressure improved?