When you say 'cleantech' most people think about energy. But as recent books like The Blue Covenant and Water Wars point out, the demand for clean water may turn out to be a bigger and more immediate challenge. Potable water is needed for everything -- not just for human consumption and agricultural use, but for almost every sector of the economy including the production and development of energy (a typical power plant uses a staggering 136 billion gallons/day or 25 gallons per kWh).
As energy demands increase and more freshwater glaciers melt, there will inevitably be a point at which we simply cannot meet our needs for potable water. The ongoing dispute between Georgia, Florida and Alabama over water resources is a reminder that this is not a problem for some distant future, but rather an immediate issue we need to address now. Countries in the Middle East have experienced water shortages for decades and so have been at the forefront of desalination technology. But the process of extracting salt out of water has required tremendous energy resources.
Until now. Major progress has been made in the desalination and purification of water, but the real breakthroughs are happening in the field of nanotechnology. Much of the energy demand of a typical 'desal' plant come from the need to intensely pressurize the water, forcing it through a typical filter, then repumping and repeating the process. A filter made of carbon nanotubes, microscopic "straws" which selectively push away negatively charges salts, require only the gravity.
I recently interviewed the CEO of a cleantech start-up company in Silicon Valley called Porifera, which is set to produce carbon nanotubes designed for desalination. He explains how it works and the many benefits of water purifying technologies.