Odd pressure problem

Hi All,

My sister has a rental house that is suffering some pressure issues.

She told me that a former tenant was complaining about the pressure, but never did anything about it. I do not know the age of the house, but I am sure I can find out. I also do not know what the supply lines are made of, however, I will be there tomorrow to install a new water heater, so I will find out.

The issue is things like the bathtub has super low water pressure, until you run the sink. With the faucet turned on in the tub, the water just trickles out. If you then turn on the sink faucet, the tub gets more water pressure.

Baffled me, so I thought I would come to the experts.

I would appreciate any ideas.

(City water supply BTW)

Some faucets can create a cross-over. It may be when that is turned on, the plugged line to the tub is now being fed partly through the sink's line. Bet they have trouble controlling the temperature!

There may be some galvanized iron pipes - could be endemic all through the house, or maybe just a nipple. If you're lucky, it's just a nipple, and you can replace it with a brass one and be done with it. If all the pipes are galvanized, it's time to repipe, which can be quite costly.