Hey Jim,
The problem maybe with the water going into the water heater. Call a licensed Master Plumber find out if they can perform a water test on your drinking water, do you have a well? It sounds like a bateria problem in the well, maybe an iron issue, but like I said get a water test done by a reputable firm. None of these fly by night companies, make sure the equipment they want to install is a quality company ( Cuno, Maclean )get a firm quote, most Flat Rate companies will insist on giving you a quote,then make sure a Master plumbing does the installation. Good luck my friend.