For reference, here's our layout in our townhome:
1st floor - Shower, sink, utility sink
2nd floor - Kitchen sink
3rd floor - Tub, two sinks, shower (same room)
Our water pressure is fine house-wide running any tap or machine (dish washer, washer) except if we run the tub. About two weeks ago, the tub tap started acting strange with an abrupt change. Both the hot and cold tap are affected by this.
If we turn on the hot/cold/both for the tub, water pressure sustains a normal rush for about five seconds. After that the pressure rapidly tapers off to about 10% of what it normally would be. After the pressure drops, all other taps on the 2nd and 3rd floors are a strong dribble at best. Taps on the 1st floor are about 50% normal. If the shut the tub off, water pressure rapidly (a couple of seconds) builds back up on the other taps. If the turn the tub back on we get the quick rush of normal pressure that tapers off again just as rapidly and drops pressure throughout the rest of the house.
Trying to apply my electronics training to this (water and electricity are similar in theory, but don't mix well in reality.), and am stumped.