Scientists are developing toilets that do not use water. Water is a limited resource, but each year 1.5 trillion gallons of clean drinking water are flushed down toilets in the United States.

Three promising types of waterless toilets are solar toilets, composting toilets, and bio-toilets. Each of these toilets recycle human waste into something useable.

Solar toilets burn up waste using the energy of the sun. Waste is cooked until it becomes a charcoal-like substance called “bio char,” which can be used as fertilizer.