Today is World Water Day. This marks another year when water gets less attention than oil, and the coming crisis becomes more severe.

Through the Middle East and parts of America and Asia, water is a physical scarcity.

In Africa and other parts of the southern hemisphere, water is an economic scarcity, which means an adequate supply is not economically feasible.

Ban Ki-moon warns: "A shortage of water resources could spell increased conflicts in the future. Population growth will make the problem worse. So will climate change. As the global economy grows, so will its thirst. Many more conflicts lie just over the horizon."