Note: This month's column was written by my business partner, William C. Carter, PE.

Most of us think very little about the large white tank in our basement or closet, but there are ways to make it last for a long, long time. A water heater's average life is eight to 12 years, but it could be 40 or more. Here's how.

Inside the water heater is either a gas burner or an electric heating coil. Water flows in and out from pipe fittings on the top. On the outside are a blow-off valve and pipe and a drain valve. Inside, the fill pipe has a long plastic pipe called a "dip tube" that takes the cold water to the bottom.

Because there are dissimilar metals inside the tank, the water makes the tank into an electric battery. The tank is "glass lined" with a coat of enamel to prevent rusting, but eventually a chip will develop or a thin place will occur in the enamel, and rusting will begin.

To prevent the tank from rusting, an aluminum or magnesium rod called an "anode" is inserted from the top. The anode corrodes, leaving the steel tank rust-free. When the anode is consumed, rusting of the tank will follow. Most anodes last four or five years, and a year or so less if you have a water softener.

The anode is replaceable. All anodes have a 1 1/16-inch hexagonal head and can be unscrewed (after partially draining the plumbing system to just below the top of the water heater). Be sure to turn off the gas or electricity before starting any work. Unscrew the anode and replace it with a new one. (It will be very tight). If space is limited above the water heater, some anode rods have chain-like connectors so you can snake it in.

To find an anode, you will have to go to a plumbing supply store like Ferguson, or Reeves Weideman. Why not a home improvement center? Most people don't even know that anodes exist, and sales would be poor. And your plumber probably won't tell you about anodes, because plumbers make a living replacing water heaters. But they will replace the anode if you ask.

While you're servicing the water heater, it is good practice to drain the water heater to flush out the sediment and scale.

Graphic courtesy of chilipepperapp.com.