One in four major cities won't be able to provide clean water to residents

From Mumbai to Sio Paolo, safe water supplies are precarious. Research suggests that conservation could be a cost-effective solution

They are two of the biggest cities in the world and both are set to grow significantly over the next decade, yet Mumbai and Sio Paulo are still unable to supply the clean and safe water residents need.

Precarious water supplies are nothing new in Sio Paulo but today Brazil's largest city is suffering the worst drought since records began in 1930. This urban crisis is being replicated across the world, with one in four of the biggest cities experiencing water stress.