First, you have to filter out all of the solids and other gunk in the water. Then, in a process called reverse osmosis, you filter out the tiniest of particles. And as an extra precaution, the water is often flashed with ultraviolet light to sterilise pathogenic microbes. "We can supply water in a very pure state – purer than what they currently get out of reservoirs and rivers," Scales says.

But inevitably, there's a "yuck" factor. Recently, psychologist Paul Rozin of the University of Pennsylvania in the US and a team of researchers surveyed 2,000 Americans, finding that while 49% were willing to try recycled wastewater, 13% refused, and the rest weren't sure. For some people, no matter how much you tell them the water is safe to drink, the feeling of disgust is too much to overcome – even in the direst of situations.

Political problem

In 2006, for example, a drought-stricken city in eastern Australia named Toowoomba tried to implement wastewater recycling. But the effort was a political disaster, as 62% of voters rejected the plan in a referendum. "Water recycling is enormously powerful, but it's politically a real problem," says Scales.

Dwindling water supplies forced Toowoomba officials into a desperate situation, and they tried to introduce wastewater recycling without giving people time to get used to the idea, says Clare Lugar, a spokesperson for the Water Corporation, the water company for Perth and Western Australia – a region that's been experiencing drought for 15 years. The corporation has been integrating wastewater recycling into its own supply. But it's taking a lesson from Toowoomba and going slowly.