Chapter 1


Mexico City is the cultural, economic, and industrial center for the nation. With a population approaching 20 million, roughly equivalent to the entire state of Texas or New York, it has become a magnet of growth. There is a continuous migration of people from rural areas to the city in search of work and the general economic benefits generated from the centers of political power. Many of these immigrants settle illegally in the urban fringe with the hope that the government will eventually provide public services.

The provision of water and wastewater service for the growing population of Mexico City presents a formidable challenge. Like the air pollution problem that received considerable attention 10 years ago, the water supply situation in Mexico City is now nearing a crisis. Continued urban growth along with poor system financing have limited the government's ability to expand the water supply network to under-served areas, repair leaks, and provide wastewater treatment. Almost seventy-two percent of the city's water supply comes from the Mexico City Aquifer, which underlies the metropolitan area and which is being substantially over-exploited. Ground water levels have been declining over the course of the past century, resulting in regional land subsidence. This subsidence which has lowered the city center area by an average of 7.5 meters, exacerbates the flood-prone conditions of the city and has damaged the infrastructure-including water and sewer lines. These difficulties, combined with inadequate hazardous waste management, leave the aquifer and the water distribution system vulnerable to contamination with consequent risks to public health.

This growing urgency very recently has resulted in the development of new laws and conservation efforts, education programs, and innovative solutions such as the privatization of water service and treatment. Reversing past trends and implementing new conservation strategies-including comprehensive metering, billing, and enforcement-will be difficult.

Like Mexico City, many of the major cities throughout the world face uncertain prospects for providing a safe, reliable water supply. The sustainability of an urban water supply depends on the physical capacity of the hydrologic system; the vulnerability of the system to contamination; capabilities of the infrastructure for treatment, distribution, and disposal; and the social, economic, and institutional aspects that influence a society's ability to manage its resources.

This report broadly covers several topics relevant to the sustainability of a water supply for Mexico City. Chapter 2 introduces the Mexico City Metropolitan Area that is the focus of the study. Chapter 3 reviews the hydrogeological characteristics of the southern portion of the Basin of Mexico where Mexico City is located, and discusses the history and consequences of ground water exploitation. Chapter 4 describes the various sources of water supplying Mexico City, the operation of the distribution systems, water treatment, wastewater treatment and disposal, and water reuse programs. In Chapter 5, the vulnerability of the aquifer to microbiological and chemical contamination is explored, and the concerns for drinking water quality and health are examined. Chapter 6 considers the potential for demand management approaches to achieve more equitable water service and fiscal stability. Chapter 7 includes a description of the recent changes in water policy and law as the committee understands them, and an examination of some of the institutional challenges for more effective water quantity and water quality management.

The report identifies several areas in which specific progress has been made, and where opportunities exist to improve the balance of water supply, water demand, and water conservation. It is concluded, in Chapter 8, that more attention should be given to managing water demand through metering and pricing mechanisms, education, conservation, and water reuse programs. A more comprehensive and integrated research program is needed to understand better the regional hydrology. The treatment of municipal wastewater prior to disposal should be a high priority, and a comprehensive, ground water protection program is required. Suggestions are given to facilitate the institutional changes currently taking place, which-if successfully implemented-have the potential to promote a new cultural perspective on the value of water. In addition to this bilingual report that summarizes much of the information developed in the course of the study, a separate and more detailed report in Spanish is published by the science and engineering academies of Mexico (AIC-ANIAC, 1995).

A study of this nature cannot identify specific technical designs, nor can it delineate specific strategies for necessary institutional and social change. The issues and related recommendations presented are meant to give general guidance as the policy makers attempt to implement the various new programs to manage the quantity and quality of water resources in the Mexico City Metropolitan Area.

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Copyright 1995 by the National Academy of Sciences. All Rights Reserved.