Risks and integrated management of the urban water cycle in megacities of the developing world: Mexico City

This paper describes the urban water cycle in Mexico City as an example of the challenges to managing water in a megalopolis in the developing world. As happens in several cities, water quality in Mexico City is affected not only by its use but also from pollutants coming from non-point sources such as air and soil. Cities, as shown in the example, can have an important impact on water resources located far beyond their geographical area. To avoid negative effects produced by the urban use of water in megalopolises several types of measures that go beyond the simplistic approach of using wastewater treatment plants to control pollution are proposed. Some of them include new concepts which also consider that treated effluents may become indirect sources of water. Therefore it is important to perform truly integrated management of water, including air and soil management in cities. The Mexico City study case illustrates water management requirements for a city of 21 million inhabitants that is not only overexploiting the local aquifer, but also relying on different basins to meet its water requirements. Because the amount of water used is very large, the amount of wastewater produced is also large, and its disposal - without any treatment - is resulting in non-intentional reuse for human consumption. In the long term, in order to address its own needs as well as prevent negative impacts in other places, Mexico City will need to perform integrated management of its water.