MIT researchers have developed an innovative water harvester that can extract clean drinking water from the air, even in extreme climates, without requiring external power or filters. The device's core is a vertical panel made from a special hydrogel material. This hydrogel is designed to resemble a sheet of bubble wrap, with small, dome-shaped structures. These domes swell and expand as they absorb water vapor from the air, increasing the surface area for moisture capture. Unlike many other water harvesting systems that rely on electricity or solar panels for power, MIT's device operates entirely passively. It leverages natural temperature fluctuations between day and night. As the hydrogel absorbs moisture during cooler periods (typically at night), the captured water vapor is released as the temperature rises (during the day). This released vapor condenses on a glass surface that encloses the hydrogel panel. The glass chamber is coated with a cooling polymer film, which aids in the condensation process. The condensed water then flows down and out through a tube, ready for collection as clean drinking water. It also addresses a common problem in hydrogel-based systems: salt contamination. Other designs often use salts within the hydrogel to enhance absorption, but these salts can leach into the collected water, making it undrinkable. MIT's team solved this by incorporating glycerol, a liquid compound, into their hydrogel. Glycerol naturally stabilizes the salt, keeping it locked within the gel and preventing it from crystallizing and escaping with the water. The hydrogel's microstructure also lacks nanoscale pores, further preventing salt leakage. The device has been successfully tested in Death Valley, California, one of the driest places in North America. Even in very low-humidity conditions (as low as 21% relative humidity), the system was able to produce between 57 and 161.5 milliliters of drinking water per day. This performance surpasses many other passive and even some actively powered water harvesting designs. While a single, window-sized panel produces a modest amount of water, the researchers envision deploying an array of these vertical hydrogel panels to provide enough water for an entire household, even in arid desert environments. The water production is expected to increase with higher humidity levels, making it effective in temperate and tropical climates as well.