There are many places in the world that have limited sources of potable water, whether because of limited rainfall or polluted water sources. Without sufficient potable water, the health of possibly billions of people remains at risk.
For example, Lima, Perú, is the second-largest capital city located in a desert. With a population of 8.5 million and an average annual rainfall of just half and inch, potable water supplies are of critical concern to those outside of the municipal water distribution system. At the same time, Lima does not lack in humidity, averaging 83% year-round, including morning fog almost daily and week-long stretches of overcast skies. This is where fog harvesting comes in to provide potable water from thin air. Actually, the idea isn’t new. For millions of years, some very specialized plants and insects have been harvesting water directly from the air.
For human beings though, who have no such specializations, we turn to technology and materials sciences. A recent project we covered in Lima, erected by the University of Engineering and Technology, utilizes air-conditioner coils to drop the air temperature below the dew point, forcing potable water out of the air into a receptacle. Still, the system is somewhat energy intensive, so it wouldn’t be of much use in areas with little to no access to reliable electricity.
Here’s a video of a typical mesh fog harvester in operation:
A couple of years ago, we covered a Massachusetts Institute of Technology [MIT] fog harvesting invention was was very cheap, used no power supply of any kind, and was fairly effective recovering humidity from the air. Now, it seems that MIT has improved on the design, making it possibly five-times more efficient. The original fog harvester consisted of a fine mesh that collected humidity, but didn’t absorb it. Once water droplets were large enough, they would run down the mesh into a receptacle, yielding potable water. Here’s a video of MIT’s latest fog harvester – much more efficient:
Over various iterations of the design, MIT was able to identify and address three main factors affecting the efficiency of the device – filament thickness, spacing, and coating. The latest design looks essentially like a standard window screen, only much smaller in scale. Each stainless steel filament, a few times the thickness of a human hair, is dipped in a coating that allows water droplets to flow more easily and then woven into a mesh. The new design is about five times more efficient than previous designs and other alternatives, with the added benefit that it requires no power and minimal cleaning.
Image © MIT