It looks like the nipple at the cold water inlet of your water heater snapped. This nipple is a threaded check valve made of black plastic. The hot water outlet also has one, just turned in the opposite direction. My hot water outlet check valve cracked and I broke it completely off trying to remove it with a wrench. Get a $9.50 Pipe Nipple Extractor Set HDX167 at Home Depot. Harbor Freight has a similar set. Getting the check valve out with this is a breeze. I replaced the plastic check valve with a brass one I found at my local RV supply store.