Appliances in your home use one of the following sources of energy to perform mechanical functions: solar, oil, natural gas, liquid propane or electricity. If you are concerned about energy efficiency and you are considering purchasing a water heater, a heat pump water heater may be a solution for you. Heat pump water heaters need electricity to work and can save you more than 60 percent of energy costs. If you are really trying to be friendly to the environment, you can purchase a water heater that uses solar energy. You can save up to 90 percent of your energy costs with this type of water heater.