According to the United Nations, 1.2 billion people live in areas of physical water scarcity and another 1.6 billion people face economic water shortage or lack the infrastructure to take water from rivers and aquifers, making water scarcity one of the most significant global problems to be faced this century. Climate change is worsening the issue and the effects are already being felt, even in the United States: The current California drought reduced the state’s hydroelectric power generation, leading to an additional $2 billion in electricity costs and a 10 percent increase in carbon dioxide emissions.
Researchers at Harvard University are turning to nature for solutions. Chemist and materials scientist Joanna Aizenberg and her team created a hybrid material based on three evolution-produced designs: the bumpy shell of the Namib desert beetle, the V-shaped spines of cacti, and the slippery coating of carnivorous pitcher plants.
The researchers are working to facilitate and control “dropwise condensation” – or collecting water on a surface as quickly as possible while also moving that collected water away. Their paper, published in Nature, explains its significance and challenges: "Controlling dropwise condensation is fundamental to water harvesting systems, desalination, thermal power generation, air conditioning, distillation towers, and numerous other applications. For any of these, it is essential to design surfaces that enable droplets to grow rapidly and to be shed as quickly as possible. However, approaches based on microscale, nanoscale or molecular-scale textures suffer from intrinsic tradeoffs that make it difficult to optimize both growth and transport at once."
The team’s biomimetic material was inspired by the geometric properties that allow the beetle shell’s bumps to promote condensation, and combined those aspects with patterns similar to those used by cacti to guide the flow of harvested water droplets. The authors explain that “the negligible friction of the slippery coating of pitcher plants inspired [them] to coat the bumps with molecularly smooth lubricant,” to further enhance water’s ability to move along the material.
"We further observe an unprecedented sixfold-higher exponent of growth rate, faster onset, higher steady-state turnover rate, and a greater volume of water collected compared to other surfaces," wrote the co-authors. "We envision that this fundamental understanding and rational design strategy can be applied to a wide range of water-harvesting and phase-change heat-transfer applications."
Meanwhile, Austrian industrial designer Kristof Retezár has developed a set of water bottles that condense the humidity in the air to collect drinkable water. FONTUS self-filling water bottles are available in a stand-alone model, AIRO, and as a bicycle attachment, RYDE. Both use solar power to power small systems inside the device that facilitate condensation.
"The idea was to solve a global problem: water issues in areas of the world where there is very little groundwater but very high humidity," Retezár told Live Science. "My intent was to invent a machine or device that would be able to filter the humidity in the air and turn it into drinkable water."
"You always have a certain percentage of humidity in the air, it doesn't matter where you are — even in the desert. That means you would always potentially be able to extract that humidity from the air," Retezár added. "Basically, you're taking air in a vapor state and converting it into a liquid state."
"The water you get is clean, unless the air is really contaminated," Retezár said. "We're thinking about making a bottle that also has a carbon filter, and this one would be for cities or areas where you might think the air is contaminated. But originally, this water bottle was thought to be used in nature, and places where you wouldn't have contaminated air."
Retezár said that the device can produce 0.5 quarts (0.5 liters) of water in 1 hour in ideal conditions, which means temperatures between 86 degrees and 104 degrees Fahrenheit (30 to 40 degrees Celsius) and between 80 percent and 90 percent humidity.
FONTUS AIRO is also still under development; it will use an inverted ventilator to suck air into the system. Retezár aims to launch a crowdfunding campaign in March to bring the devices to market, and hopes to keep the retail prices under $100. If all goes according to plan, the self-filling bottles could be commercially available by the end of 2016.