Getting enough water is one of the greatest challenges in human spaceflight. As its mission objectives have become increasingly more ambitious, NASA has been at the forefront of water purification technology. Designers of water purification systems for space travel face many of the same challenges as designers of systems for use in developing nations, and many of the purification systems developed by NASA have been adapted for use here on Earth. Water purification technology from the Apollo lunar missions has been successfully commercialized, and a system based on the Space Shuttle's water purifier is widely in use in developing nations today. Currently, NASA is developing even more advanced water purification systems for use on the International Space Station and future outposts on the Moon and Mars. While this most recent technology is more advanced than necessary for most current applications, it may still eventually contribute to making people's everyday lives better right here on Earth.
Introduction

NASA/www.nasa.gov/
Figure 1: A NASA rocket.
The Need for Water Purification
Getting enough water is one of the greatest challenges in human spaceflight. Human beings cannot survive without water, but water is heavy and it occupies a large storage volume. In the early days of human spaceflight, when missions lasted only a few hours or at most several days, it was possible to launch space travelers from Earth with all of the water they needed. However, as mission plans lengthened, bringing water from Earth to sustain human life for extended periods became less feasible. Instead, researchers began to develop water purification technology to recycle the limited water supply that could be provided.
While astronauts face challenges in getting enough water to survive in space, many more people have the same problem in developing nations down here on Earth. According to the World Health Organization, 1.1 billion people, or 17% of the global population, lacked access to a safe water source in 2002. Interestingly, designers of water purification systems for space travel face many of the same challenges as designers of systems for use in developing nations. The key features of equipment suitable for both settings are durability, simple design, and low maintenance requirements. Obtaining specialized parts or personnel experienced in water system repair can be equally difficult in space and in developing nations. Given these similarities, water purification technology designed for NASA can be very useful to developing nations if the right adaptations are made to it [12].