the energy of a thermal power station not utilized in power production must leave the plant in the form of heat to the environment. this waste heat can go through a condenser and be disposed of with cooling water or in cooling towers. if the waste heat is instead used for district heating, it is called cogeneration. an important class of thermal power station is that associated with desalination facilities; these are typically found in desert countries with large supplies of natural gas, and in these plants freshwater production and electricity are equally important co-products.