Dear Ida B. Green,
You wrote recently that you should replace your water heater if the anode rod has been totally eroded. This isn't how I understand the use of this "sacrificial rod."
The anode rod is almost always overlooked but is key to the longevity of your water heater and its liner. If it has been completely eroded for a period of time, you have reason for concern and should be looking seriously for other signs of a deteriorating liner.
An anode rod is made of magnesium or aluminum, shaped around a steel wire and screwed into the top of your tank. If you have one rod in your tank, you probably have a six-year warranty. If you have two, probably a 12-year warranty. Depending on your hot-water temperature setting, the amount of water you heat and the softness of your water, the rod may need to be replaced anywhere from every six months to four years. It's a good idea to check it annually and replace it when 6 inches or more of it are eroded.
Look at your owner's manual or check "anode rod" online to decide whether to make this a do-it-yourself project or to hire a plumber. Either way, it's cheaper and it's greener to check and replace your anode rod than to dump and replace your water heater.
Keep it Green,