Watch on HDtoday. Can a región of 22 million people become water sustainable? Mexico City was not built near water, but in the middle of a lake. To supply it with fresh water, it is necessary to bring it from other states. In addition, once sewage water leaves the city, it ends up in the state of Hidalgo to be used in agriculture. This is an environmental case study of the Valley of Mexico and its struggles to save itself as the population grows.