Once a year, everyone should drain a bucket of water from the hot water heater tank to remove sediment that lowers the efficiency of your heater. Of course, always follow the manufacturer's instructions, or you can try the instructions found here. One detail that needs to be stressed: never drain more than 1/4 of your hot water tank unless you have turned off the hot water heater.
Why, you ask, is there sediment in the bottom of my hot water heater?
Sediment is solid material that doesn't dissolve in water. There might be sand, grit, or other stuff that has gotten into your hot water heater. If this happens, this material will tend to settle out in your hot water heater tank, right down near the bottom by the heating element. If the heating element gets covered up, then the sediment is getting most of the heat, rather than your hot water, which is definitely not energy-efficient.
On the other hand, if you do this one year and no sediment comes out, then you can skip this the next year.
We never know the worth of water till the well is dry.