Heating elements are used in an electric water heater to convert electrical energy into heat and transfer it to the water. Since elements come in direct contact with water, they must be insulated well.
In an electric water heater, electricity flows through a wire in the element designed to provide enough resistance to heat it. The metal casing around the element warms, and water in the tank absorbs this heat. Since they remain covered in water at all times, elements must be able to resist corrosion.
Hard water, which contains a relatively high concentration of sediments, can build on elements, so homeowners in regions serviced by hard water may need to look for elements specifically designed to handle it.