Look in the mountains to the west of Tucson and your eye will be drawn to a set of shimmering rectangles that dominate the valley floor. These are not solar panels, nor parking lots, nor any nefarious construction. They are immense pools of water, part of the Central Arizona Project. Tucson’s need for water has greatly exceeded the capacity of the area, so a vast network of canals brings Colorado River water to the state. Here it is released into vast holding ponds – and it is allowed to infiltrate into the ground. The loose rock filling this valley is slowly refilling with groundwater, filtering the water brought to us from far away. It is no small feat first to have defeated one aquifer, then to have tamed another river system to recharge the first – but we are doing it, for better or worse.