At least once a year, drain water from the hot water storage tank. Over time sediment/mineral deposits will build up at the bottom of the water heater. This can lower water heater efficiency and cause damage to heating elements in electric water heaters. Continued sediment/mineral deposit buildup in your water heater will also cause damage to the storage tank itself over time resulting in lowering the life of your water heater.
Water heaters that show any signs of rust either at the top or especially the bottom of the water heater is a sure sign that your water heater is going to leak at some point in time. Many times we have been called to homes during holidays, etc to replace rusted out water heaters. The old saying that "if it can happen, it will" is a word to the wise when facing a rusting water heater!!! These should be replaced to avoid waking up to a flooded house from a busted or leaking water storage tank!!!!
At least once every two years, have your water heater inspected by a service technician. He or she will also check the drain valve for signs of leakage.