A worker tries to lift up a weak cow from among the carcasses of drought-stricken cows 50km (31 miles) east of the capital Nairobi, September 16, 2009.
Here's a thought that should blow your mind: there are more mobile phones in the world than there are toilets. That's just one part of the global threat of water scarcity, but far from the only one. Approximately one in nine people in the world lack access to an improved water source, leading to easily preventable disease and reduced agricultural yield. The freshwater supplies we have are threatened by pollution and overuse, while climate change could lead to severe droughts in already water-stressed areas like the American Southwest and sub-Saharan Africa. The good news is that there is more than enough water to go around, even for a growing population. The challenge in Rio is how to ensure that nine out of nine people have the water they need.