The source of the problem is clear: greater demand for biofuels, intended to reduce emissions from fossil fuels, requires massive increases in irrigation in productive but relatively arid American farmland.
The film takes place in a parched, near-future Australia, where the control of water is the greatest power. As it happens, over the past 20 years Australia has weathered one of the most devastating droughts on the planet.
It almost never rains in Lima, the capital city of Peru, making it especially vulnerable to water shortages. The surprising solution might be reviving a system of ancient canals that date back to even before the Incas.