Hot Water Heater Flushing
Manufacturers recommend flushing your hot water hear every one to three years depending on the model and water source. This helps to control the buildup of mineral deposits that can sometimes cause discolored water or odor issues. Flushing also keeps your water heater operating efficiently, which usually can extend the life of the heater.
There are several good links about how to flush a water heater that you can access from the links below.
Sources for more information on flushing water heaters
WIKI HOW: http://www.wikihow.com/Flush-a-Water-Heater
Home Depot: http://www.homedepot.com/c/water_heater_maintenance_HT_PG_PL
Manufacturers normally have flushing information online.
If you are uncomfortable with flushing your heater, plumbing professionals can provide this service.