Development has made precipitation a problem. All our hardscapes prevent rain from percolating into the ground. Ditches and curbs concentrate the flow and pipes either take the rainwater to a wastewater facility to be processed (using chemicals and energy) or to rivers where the strong pulses of water erode the banks. And all along the way, the precipitation picks up the crud of urban life: litter, oil from the roads, and pesticides from yards.
As a partial solution, engineers have come up with an inexpensive way to filter stormwater, cleaning many of the contaminates out. This could mean that water getting to our rivers would be cleaner. In the developing world, it could become a source of water.