You may have gotten some advice at one time or another about draining your water heater periodically. Your neighbor might have mentioned it, or you may have even seen it recommended by the manufacturer of the water heater. But why do you need to do this, and how is it done?

As to the why, the answer is sediment. Sediment is small bits of dirt, rock and other debris that can work its way into your water heater over time. Being heavier than water, it will settle to the bottom of the tank and build up. It's not an earth-shattering problem, but in areas having water with a high mineral content, or water coming from a well or other supply that may not be well filtered, it certainly is possible to accumulate a fair amount of material in the bottom of the tank.

That sediment buildup can potentially decrease the amount of hot water the tank can hold, or it can clog up the drain valve. If your city periodically flushes the municipal water lines, or anything else causes a water surge or a sudden increase in water pressure, that layer of sediment can get itself all stirred up and work its way into faucets, valves and other areas where it's better off not being.

Hence the advice to periodically drain and flush your water heater to remove that buildup of sediment before it can do any harm. This is a very simple procedure, and how often you need to do it depends on your local water conditions -- annually or even semiannually in areas with poor water quality or if you're on a well, and every couple of years in areas with very clean water or homes with a filtration system.

FLUSHING YOUR WATER HEATER

First of all, shut the power. If you have an electric water heater, simply shut the circuit breaker. Don't overlook this step, because if the elements come on while they're not covered with water, it can do some serious damage. For a gas water heater, shut the valve controlling the gas supply to the heater.

Next, shut the cold water supply to the water heater. This is a valve that is located above or next to the heater. Go inside the house, open the hot water faucet that is closest to where the water heater is, and wait a moment until no more hot water comes out.

Near the bottom of the water heater is a drain valve. It may be white plastic, or it may be a brass valve that looks like an outdoor hose bib. Attach a garden hose to the valve, and route the other end to a safe location. Remember that this is very hot water that will be coming out of the hose, so keep it away from kids, pets and sensitive plants.

If your water heater is located in a basement and you have nowhere to route the hose -- to a sump or floor drain, for example -- then the draining process will need to be done with a bucket, and will obviously be a whole lot more tedious. To avoid burns, use a sturdy, good-quality bucket, and don't fill it more than half full.

Open the drain valve all the way, and let the water heater drain. This will typically be a relatively slow process. You may find it necessary to open the pressure relief valve on the tank to encourage things to get started, something akin to punching a second hole in the top of a can to get it to drain.

To get an idea of how much sediment is in the tank, you can run some of the hot water into a large glass jar (carefully). This is a good indicator of what was in the tank, and if you know how long it's been since the last time it was drained, it can give you a rough idea of how often you should be doing this.

When the tank is empty, shut the faucet in the house and turn on the cold-water supply valve. This will allow fresh cold water to run through the tank, stirring up and flushing out any remaining sediment. Unless you have a tremendous buildup of material in the tank, it shouldn't take more than about five or 10 minutes to completely flush it out.

When the water is clear, shut the drain valve and remove the hose. Leave the main cold-water supply valve open and refill the tank. When the tank is full -- and only when it's full -- you can turn on the electricity to reactivate the elements, or turn on the gas valve and relight the pilot. If you are unsure about how to safely relight the pilot, call your gas company for assistance.