Researchers at the University of Buffalo in New York have found what they say is an efficient and inexpensive way to turn saltwater and contaminated water into potable water.

The idea is described in a study published online in the journal Global Challenges.

Floating solar still prototype.Using low-cost materials, researchers created a system that maximizes the use of solar energy during evaporation, while minimizing the amount of heat loss during the process.

As part of the research, the team built a small-scale solar still. The device, which they call a "solar vapor generator," cleans or desalinates water by using the heat converted from sunlight. The sun evaporates the water.

During this process, salt, bacteria, or other unwanted elements are left behind as the liquid moves into a gaseous state. The water vapor then cools and returns to a liquid state, where it is collected in a separate container without the salt or contaminants.

According to researchers, people lacking adequate drinking water have used solar stills for years; however, these devices are inefficient. For example, many devices lose heat energy due to heating the bulk liquid during the evaporation process. Meanwhile, systems that require optical concentrators, such as mirrors and lenses, to concentrate the sunlight are costly.

The UB-led research team addressed these issues by creating a solar still about the size of mini-refrigerator. It is made of expanded polystyrene foam (a common plastic that acts as a thermal insulator) and porous paper coated in carbon black. Like a napkin, the paper absorbs water, while the carbon black absorbs sunlight and transforms the solar energy into heat used during evaporation.

The solar still coverts water to vapor efficiently. For example, 12% of the available energy was lost during the evaporation process, a rate the research team says it believes is unprecedented. The accomplishment is made possible, in part, because the device converts only surface water, which evaporated at 44 degrees Celsius.

Based upon test results, researchers say the still may be capable of producing 3 to 10 liters of water per day, an improvement over most commercial solar stills of similar size that produce 1 to 5 liters per day.

Materials for the new solar still cost roughly $1.60 per square meter—a cost that could decline if the materials were purchased in bulk. (By contrast, systems that use optical concentrators can retail for more than $200 per square meter.)