Turn the manual shut-off valve to shut off the gas supply to the water heater. If you have an electric water heater, turn off the power to the unit.
Secure a garden hose to the drain valve and place the other end over a drain.
Turn the cold water valve to shut off the cold water supply.
Locate the temperature pressure relief valve at the top of the water heater. Lift the lever handle of the valve.
Wait for the water to flush out of the heater. Allow the water tank to completely drain. Release the lever handle.