How do you know when your water pump on your 1995 Chevy Lumina is bad?

One way is: with a cold engine, take off the radiator cap, start the engine and let it run to operating temp, and look into the radiator to see if you see any coolant flowing usually from one side of the radiator to the other. If you look in the radiator and the coolant is not moving, then your water pump is probably gone, and don't overheat your engine. Without coolant flowing through the engine you cna overheat the engien and cause severe damage.