One way to produce clean water is to heat dirty water until it turns into steam. As the steam rises, it leaves behind the heavier contaminants and can be collected and cooled, providing clean water. There are many ways to heat water, one of which is to use light-absorbing materials at the air/water interface to harvest sunlight and convert the light into heat. This method is very energy-efficient because all of the absorbed solar energy is used to heat water near the surface, rather than heating the entire body of water.