Sometimes it becomes necessary to drain a water heater. Draining a water heater once per year or so can help keep too much sediment from building up inside of the unit. You will need to drain the water heater to replace heating elements in electric water heaters. Obviously, if you are replacing the entire unit, you will need to drain it first. Because of having to repair many water heaters, I have discovered that this process will take about a hour or more to drain and refill your water heater tank.
Turn off the power to the water heater.
On both electric and gas models, it is important to make sure that the power has been shut off. If you have an electric water heater, the elements will burn out in less than a minute if you leave them on with no water in the tank. Likewise, it is not good for the life expectancy of the water heater if the gas burner comes on at the bottom of an empty tank.
Attach a hose to the valve at the bottom of the unit.
Find the faucet at the bottom of the water heater. It will look like the outside faucets on the side of your house. This faucet is designed so that you can screw a garden hose on to it. Attach the hose and position it so that it will drain outside or into a drain inside your home.
Turn off the incoming cold water source.
At the top of the water heater, you should have a valve on the cold water line that feeds into the unit. Turn the valve until the cold water has been shut off. If there is no valve on the cold water, you will have to shut off the water coming into your house. This may require a trip to the water meter.
Open a hot water faucet to relieve the pressure.
A bathroom or kitchen sink will usually be the best choices for opening a hot water faucet. It should run for less than a minute if you have successfully turned off the cold water into the water heater. If the water keeps running in a steady stream, you will have to find out why the water has not been turned off. Leave the faucet open until you are ready to refill the tank.
Open the valve on the bottom of the water heater.
With the water off and the pressure relieved, open the valve on the water heater to let the water start to drain through the hose. It will flow slowly but steadily until the tank has been emptied.
When the water stops flowing, turn off the valve.
It may take more than 30 minutes to finish draining the tank. Once it is drained, turn off the valve and disconnect the hose. You can leave the hot water faucet on. This will allow the air inside the tank to bleed off while you refill the water heater tank when you are ready to do so.