The ancient Aztecs first picked the spot. They built their city atop the huge lakes that filled this valley, leaving the natural freshwater supply intact around them. The city flooded back then too, but the Aztecs, probably the last civilization to properly manage this watershed, built a system of dikes to control the problem.
The “historic mistake” kicked in around the 1600s, when Hernándo Cortés and his band of conquerors arrived. To make room for their expanding empire, over a few hundred years, they slowly but surely drained all the valley’s lakes.
By the 20th century, long after Mexico’s independence from Spain, the fresh surface water was mostly gone and the hunt for new sources had taken over. Hundreds of miles of pipes now bring in about 30 percent of the city’s water needs from faraway rivers and lakes. The rest comes from the valley’s vast underground aquifer.