On the ISS, every drop of moisture, from humidity to urine, has to be filtered and reused. But the current system is very heavy, has to be replaced every 90 days, and fails to filter out certain contaminants, according to NASA. Danish company Aquaporin A/S has developed a new system that uses proteins called aquaporins. "It is essentially the mechanism that allows water to cross the cell membrane of living cells," says Peter Holme Jensen, CEO of Aquaporin A/S. In nature, these proteins allow plant roots to absorb water from soil, and let the two human kidneys together filter about 45 gallons of fluid per day. They are also very selective, preventing contaminants from passing through.