Stupid Question About Water Pump

All the systems that I have dealt with are as described above. The pump runs through a check vavle to a tee and the city water runs through a check valve to the other side of the tee. Both of these check valves run toward the tee, which supplys all the domestic water from either source. Running the pump while having the city water on will do nothing as long as you have water in your water tank. Otherwise the pump will just keep running since it has no water to build up pressure with. If it has water it will build up pressure and stop running unless the city pressure is less than the pump set point. If that is the case, you will be using your tank water.