When your GM water pump is not working, you have a block full of rapidly heating engine coolant and nothing traveling to the radiator to cool it down. An overheated engine can lead to warped heads, blown head gaskets, and excessive wear on your vehicle.
The GM water pump directly or indirectly affects nearly all of your vehicle's systems. If your GM water pump fails, you need to replace it right away. Short of your engine overheating, there are a few other ways to determine whether you need a new water pump. If your vehicle is leaking coolant from the pump, this means the pump is working harder than it should to move less fluid. It is better to replace a leaking GM water pump than try to repair the leak. Another problem area you might find is the GM water pump pulley. This pulley should be rigid and difficult to move. If the pulley on your GM water pump moves easily, this means the bearings are worn and you should replace the pump immediately, rather than waiting for it to fail completely.