MKSLUP
When you have the hose hooked up to city water, you shouldn't turn your pump on. BTW - If you haven't already done so, pick up a water pressure regulator and hook it up to the faucet before hooking up your hose. This will prevent excess pressure from damaging your water system. You might also want to consider a water filter to hook up to the hose so you filter the water before it gets into your rig.
While on the road, I always put at least 1/4 tank of fresh water in the holding tank. If we need to use the restroom or wash our hands, we have water available. Since you're not hooked up to a water source, you have to turn your pump on to get the water to flow through the system.