California's drought has produced a plot twist too singular even for Chinatown: farmers volunteering to give up a quarter of their water. Scores of farmers in the delta of the Sacramento and San Joaquin rivers made the unprecedented offer on Friday in a deal to stave off even steeper mandatory cuts.

It's estimated that we use 9tn cubic metres of water every year. As the global population grows, it is becoming an increasingly precious resource, with millions forced to walk for more than a mile to collect their daily supply. We investigate the innovative technologies that will help tackle our water crisis in future.

Bill Gates sipping from a glass of water doesn't sound like riveting television. But add the subtitle: "This water was human waste five minutes earlier" and people will sit up and take notice.

The recent World Economic Forum Global Risks report identifies the 10 "biggest threats to the stability of the world" over the next 10 years. These are difficult times, and the catalogue of potential threats includes many that may seem familiar, including high unemployment, war and the spread of infectious disease.

As anyone who has done a survival course can tell you, we can survive weeks without food but only a matter of days without water. Of course, many of us are lucky enough to have water on tap, but according to the UN, only 42% of people in rural areas had access to clean water in 2004.