Earlier this week the New York Times published an article about how environmental issues have become a major force in political advertising during this election cycle.
Renewable Energy: An Overview - Water
Before and during the Middle Ages, the geared water mill spread from Rome throughout western Europe. The watermill was used to grind grain, saw wood and marble, and for turning grindstones. The scarcity of slaves and the value of draft animals for other uses may have accelerated its acceptance. These watermills formed the power base for civilization prior to the Industrial Revolution.
But the power produced by these mills could not be transported - it had to be used at the mill site. Not until electricity could be generated practically from falling water could this barrier to water power be broken, and by then most of the industrial world had converted to steam power.
Still, the world's first hydroelectric power plant built at Godalming, England, in 1881 signaled a new era in power and energy. This renewable technology quickly took hold and spread throughout the world. Hydroelectric power was scarcely 20 years old when Arizona began to look to it as a means to turn the desert into an oasis.
More on hydropower here.