One such solution is desalination, the process by which salt water is converted into drinkable fresh water. This involves the removal of alt compounds and other chemicals from the salt water, a process which has traditionally been carried out by heating the water (the thermal method). The main disadvantages of this method has been the cost. Consequently, a cheaper and more flexible method has been developed, whereby salt water is purified by passing it through membranes. This method is used most effectively in combination with the thermal method.