Not sure about what you are calling a water pump by pass. On all the coaches we have owned somewhere on the inlet side of the pump there should be a valve will isolate the fresh water tank from the pump. That valve should be in line from the tank to the pump. On our ACE it obscured by a wiring harness, hard to see under all the wires but it was there none the less.
2018 ACE 27.2
Toad 2019 Jeep Cherokee Trailhawk
Roadmaster Falcon All Terrain Towbar