The invention of the plastic-lined nipple is the result of the unfortunate situation between steel and copper. Steel and copper do not get along. When copper or brass touch steel, the steel will rust and corrode but the copper or brass will not. When it comes to water heater's and plumbing, this can be a problem. A water heater's tank is made of steel and many plumbing lines are made out of copper. If your water heater is brand new and was installed with copper lines running directly to it, check to see if corrosion or rusting has occurred on the water heater. It probably has not, but if it has, having some plastic-lined nipples installed would be of great value to the water heater in the future.

If you are handy with plumbing, you can install gate valves on your hot and cold lines on top of your water heater. Use brass valves and install them into plastic-lined nipples instead of directly into steel plumbing. Don't attach copper or brass directly to steel or the steel will corrode and rust. This will allow you to have positive control of your water lines at the water heater itself.

Heat traps can be used where the plastic-lined nipples are installed. Hire a plumber to do this to increase the water heater's efficiency. Make sure adapters are attached to the copper plumbing. If the water heater has a combination anode rod inside, the plastic-lined nipple will still be important. Install a plastic-lined one if at all possible. If you have a curved dip tube installed inside your water heater, you will need a three inch long plastic-lined nipple as well.

The easiest method of adding plastic-lined nipples if you have steel plumbing is as follows: Attach to both the hot and cold lines a plastic-lined nipple where the lines protrude from the wall. Attach to both of the hot and cold lines another set of plastic-lined nipples where the lines connect to the water heater. Use copper flex-connectors to connect the hot line from the wall to the water heater and do the same for the cold line. Heat traps should be installed to your plumbing lines for increased heating efficiency and to keep the water in the lines warmer.

Plastic-lined nipples may also be installed on the T&P valve. A lack of corrosion or rusting will keep the T&P working properly without getting any trapped water inside. This is not essential, but it can help.