Cover Image
close this bookWater for Urban Areas (UNU, 2000, 243 p.)
close this folder5. Water supply and distribution in the metropolitan area of Mexico City
close this folderMacro-projects
View the document(introduction...)
View the documentThe Cutzamala System
View the documentThe Cutzamala Macrocircuit and the Cutzamala ''Aquaférico''
View the documentSewage

(introduction...)

In order to supply the necessary water to the most important cities in Mexico, the federal government is committed to building more water projects in the Valley of Mexico, Guadalajara, Monterrey, and Tijuana, starting in 1997, together with the local governments and the CNA. Even though the main objective is to solve the most acute problems related to drinking water supply and sanitation in these cities, the government will have to consider seriously in the foreseeable future the management of water demand, along with supply management. There is simply no other long-term alternative.

In the Valley of Mexico, the water projects mainly involve the enlargement of the Cutzamala distribution system; the construction of two aqueducts (Macrocircuit and "Aquafco"); and covering 86 km of the currently uncovered main sewage line of the ZMCM. It was also planned to construct four wastewater treatment plants and to re-inject treated wastewater into the aquifer. However, in 1998, the newly elected government of Mexico City cancelled these plans. Several issues were considered. First, the investment costs for treating the wastewater and transferring it hundreds of kilometres from the source to the Mezquital Valley would be extremely high. Secondly, Mexico has not developed a cost-effective technology to treat wastewater and re-inject it into the aquifer. Thirdly, construction of just the treatment plants, without proper water resources management and planning, would not solve the acute sanitation problems of Mexico City and Mezquital Valley.

The total investment cost of these macro-projects would have been about US$1,800 million over a three-and-a-half-year period, including a US$500 million loan from the Interamerican Development Bank (IDB), and financial assistance from Japan, the Mexican federal government, and the governments of the states of Mexico, Hidalgo, and Mexico City (El Universal, 21 May 1997).

The Cutzamala System

In 1976, the project known as the "Cutzamala System" (Sistema Cutzamala) was planned to supply water to the ZMCM from both the Cutzamala and the Lerma-Balsas river systems (in the State of Mexico) and to reduce the over-exploitation of the aquifer of the Valley of Mexico (CNA, 1997b). The Cutzamala System is the second source of water for the ZMCM. It supplies water to the north of Mexico City and to the State of Mexico. The water has to be transferred from 60-154 km away and pumped to a height of more than 1,000 m, thus requiring 102 pumping stations, which makes this operation extremely energy intensive and expensive (SEDUE, 1990; CNA, 1997b).

Because of the magnitude of the project, its construction was initially planned in three stages. The first came into operation in 1982 (4 m3/sec), the second in 1985 (6 m3/sec), and the third in 1993 (9 m3/ sec) (CNA, n.d.b). In 1997, a fourth stage (the Temascaltepec project) was expected to be initiated. However, the government has not been able to start construction on the project owing to severe social problems (CNA, 1997b). People living in the areas that will be affected by the construction of the fourth stage have opposed the project, because they think it will supply water to the people living in Mexico City, and there is no reason why they should suffer simply because water is needed in another part of the country. To a significant extent this is due to the lack of an adequate strategy on information and communication from the governments to society and to the absence of proper public participation - the project will in fact benefit people living both in Mexico City and in the State of Mexico (CNA, personal communication). Government institutions have generally not considered the potential social conflicts resulting from the transfer of water resources from one basin to another; nor have they properly analysed the nature of the beneficiaries and the people who may have to pay the cost. In fact, not even the Environmental Impact Statement (EIS) for the fourth stage of the Cutzamala System (CNA, 1997b) mentions the social implications. Like most EISs in Mexico, it considers almost exclusively technical factors; social issues are conspicuous by their absence.

The Cutzamala System utilizes seven reservoirs and comprises a pipeline for drinking water, a regulatory reservoir, and a 127 km aqueduct, which includes 21 km of tunnels, a 7.5 km open canal, one water treatment plant (24 m3/sec capacity) (CNA, n.d.c), and six pumping stations to raise the water 1,300 m, which requires total energy of 1, 650 kWh/year (CNA, 1997b). The water is first treated at source in the Los Berros treatment plant (pre-chlorination, alum coagulation/flocculation, gravity sedimentation, and rapid sand filtration) and then it enters the Cutzamala System (National Research Council, 1995).

Initially, what was later converted into the Cutzamala System was a hydropower project. Cutzamala took advantage of the infrastructure that already existed for the hydropower, but the planned water use was changed. Currently, only 3 m3/sec is used to generate hydro-power during peak hours and to satisfy local energy requirements in the agricultural and industrial energy sectors (CNA, 1997b). The programme on drinking water, drainage, and sanitation of the ZMCM now expects to increase the water supply from the Cutzamala System to the Valley of Mexico from 0.6 km3/year (19 m3 (sec) to 0.76 km3/year (24 m3/sec), and to treat 1.3 km3/year (42 m3/sec) of wastewater (CNA, 1994, 1997b).

According to the EIS carried out for the fourth stage, the total investment cost of the first three stages was US$965 million (1996 estimates). If the estimated cost of the facilities from the cancelled hydroelectric system is added, the total investment cost becomes US$1,300 million. The reservoirs of the earlier hydroelectric plants represent a volume of 840 million m3 (CNA, 1997b).

The total area affected by the construction of the Cutzamala System during the first three stages is approximately 710 ha, with a land value of US$3.55 million (CNA, 1994, 1997b). One of the main adverse socio-economic impacts of the Cutzamala System has been the resettlement of communities, who, as of February 1999, had not received the expected compensation.

In addition to the construction of the Cutzamala System, about 190 so-called social projects have been built to benefit some of the people living in the most affected municipalities (CNA, 1994, 1997b). These projects were built jointly by CNA and the communities, and consist mainly of the construction, enlargement, and rehabilitation of both water supply and sanitation systems, as well as the construction and rehabilitation of houses, schools, and farms. Equally important is the construction and rehabilitation of roads by the CNA, both for the Cutzamala System and for social benefit. The cost of these social projects was estimated in 1996 to be equivalent to 5 per cent of the direct investment in the Cutzamala System, which would represent an additional US$45 million (1996 estimates) (CNA, 1997b).

It is worth noting that the total cost of the Cutzamala System at US$1,300 million (mainly construction and equipment costs) was higher than national investment in the entire public sector in Mexico in 1996, including education (US$700 million), health and social security (US$400 million), agriculture, livestock, and rural development (US$105 million), tourism (US$50 million), and the marine sector (US$60 million). Up to 1994, the Cutzamala System alone represented three times the annual infrastructural expenditure of the Ministry of Environment, Natural Resources and Fisheries for 1996, which was more than US$470 million (CNA, 1997b).

The energy requirement to run the Cutzamala System is about 1,787 million kWh/year, which represents an approximate cost of US$62.54 million. The total investment cost would increase significantly if the investment costs in personnel (US$1.5 million/year) as well as the water treatment process costs were added (CNA, 1997b). The energy consumed by the system, plus the energy that could have been produced if the hydroelectric system had continued to be used as originally planned, could have supplied power to a population of about 2.59 million people.

If only the operational costs for running the Cutzamala System are considered (about US$128.5 million/year), supplying 600 million m3 of water (19 m3/sec) would mean an average cost per m3 of US$0.14 and energy consumption of 6.05 kWh/m3. The latter figure is more than seven times the consumption of power of locations near the ZMCM. The price of water of about US$0.2/m3 is not enough to cover either the operational costs of the Cutzamala System or the purification or distribution costs of water to the ZMCM. According to the EIS (CNA, 1997b) for the fourth stage of the Cutzamala System, the minimum price of water to cover expenses should be over US$0.3/m3. It would be even higher if the cost of treating and distributing the water is included.

Once the fourth stage of the Cutzamala System is operating, the water supplied will increase from 19 m3/sec to 24 m3/sec. This last stage includes the construction of a reservoir with a capacity of 65 million m3 to regulate an approximate flow of 5,000 litres/sec, a 15 m3/sec pumping station, 18 km of canals, and 12 km of tunnels (CNA, 1997b).

Some studies have indicated that, if the leaks in the distribution system from Cutzamala to the ZMCM were repaired, there would be no need to construct the fourth stage of the project. This means that the additional water supply of 5 m3/sec that is being planned at very high investment, social, and environmental costs would not have been necessary had better planning and management practices been implemented. The government has so far made no public statement on this issue.

The Cutzamala Macrocircuit and the Cutzamala ''Aquaférico''

The federal government, together with the government of the State of Mexico and the CNA, is constructing two distribution lines in order to facilitate a better distribution system for the water coming from the Cutzamala System.

The Federal District is constructing an aqueduct, known as "Aquafco," that will distribute water from the Cutzamala System, which comes from the west, to the southern and eastern parts of the ZMCM (National Research Council et al., 1995; CNA, 1997d).

In the State of Mexico, the water distribution system is an aqueduct known as the "Cutzamala Macrocircuit." It is expected to be completed by the year 2000 and will be built around the perimeter of most of Mexico City to the north, carrying water to the northern, southern, and eastern parts of the city (CNA, n.d.d,e,f). The first stage of the Macrocircuit was inaugurated in October 1994. Both the first and the second stages of the Macrocircuit are now in operation, providing a continuous water supply of 4 m3/sec and benefiting 1,382,400 people by 250 litres/day/person. The third and fourth stages of the Macrocircuit will increase the drinking water supply by an additional 7 m3/sec (making a total volume of 11 m3/sec), benefiting 4,752,000 inhabitants living in the eastern and northern areas of the State of Mexico by about 200 litres/day/person (CNA, n.d.d,e,f; CNA, 1994, 1997c). The Macrocircuit includes the construction of two pipelines of 168.28 km which will connect to pipelines already built, making a total of 226.48 km. The two pipelines will need a surface area of 336.56 ha, plus 71 ha for the storage tanks (CNA, 1997c).

Total investment in the Macrocircuit between 1987 and 1997 was US$78 million, and the estimated cost for stages three and four (1997-2000) is expected to be about US$190 million, making a total investment of US$268 million. This amount represents almost 50 per cent of the total budget of the public sector at the national level for 1995 (US$563 million) in the areas of urban development, ecology, and drinking water (CNA, 1997c).

Sewage

Between the beginning of the twentieth century and 1936, parts of Mexico City were sinking by about 5 cm/year. However, higher water demand resulted in the construction and operation of deeper wells between 1938 and 1948, which increased the land subsidence rate first to 10 cm/year, and later to 30 to 40 cm/year. The functioning of the sewerage system, which until then worked on a gravity basis, was severely affected by this settlement. The network also sank with the city and its level in the different parts of the city became uneven. Consequently, it became necessary to pump wastewater up from the small sewage pipes to the level of the main wastewater collector of the city, increasing both maintenance and operation costs.

However, the increasing population in the ZMCM made the sewage collection and treatment capacity insufficient. It was then decided to build another main collector for wastewater for both Mexico City and the State of Mexico as a combined sewage and rainwater network ("Drenaje profundo"). This system is constructed up to 300 m below the ground level of the city. It is thus not affected by the sinking of the city (Departamento del Distrito Federal, 1990)

This main collector carries both rainwater (an annual average of 14 m3/sec) and wastewater (48 m3/sec) through primary and secondary networks. The secondary network is used to transport municipal and industrial wastewater and rainwater in pipes of up to about 6 m in diameter. The primary network is connected to the secondary network and stores, transports, and disposes of the wastewater into the Gulf of Mexico through four artificial channels located at the northern end of the basin (UNAM, 1997; National Research Council et al., 1995). The networks have 66 pumping stations, regulatory tanks for flow control, storm tanks, 111 km of open canals, piped rivers, dams, and lagoons, and 118 km of underground collectors and tunnels. According to 1995 figures, the total volume of wastewater discharged into the ZMCM sewerage system was 2,349,116 km3 (Departamento del Distrito Federal, 1990; National Research Council et al., 1995; INEGI, 1996).

Being located within a naturally closed hydrological basin, the city is especially vulnerable to flooding. Throughout history, artificial channels have been built to carry wastewater mixed with rainwater out of the city. The rainy season in the ZMCM is characterized by storms of short duration and high intensity, which can produce up to 70 mm of rainfall, representing 10 per cent of the total annual precipitation. Thus, the main collector was designed to carry about 200 m3/sec of water over a 45-hour period, even though it has carried up to 340 m3/sec (National Research Council et al., 1995). Such sudden fluctuations in the amounts of water that have to be drained create severe problems for the design and operation of the infrastructure.

The sinking of the city has also affected the sewerage system owing to pipe fractures and loss of the hydraulic gradient, which has significantly reduced the efficiency of the whole urban sewerage system as well as contributing to groundwater contamination. New investments include covering 86 km of the currently unlined and open main collector, which would prevent the dumping of garbage and also eliminate environmental and health risks.