Figure VII.2 Map of the wastewater irrigation system in the Mezquital Valley, Mexico Table VII.1 Irrigation data for the Mezquital Valley, 1993-94 Irrigation systems Area (ha) covered 1 Cultivated 2 No. of users Water volume (10 6 m 3 a -1 ) Production value (10 6 N$) 3 District 03 (Tula) 45,214 55,258 27,894 1,148 255 District 100 (Alfajayucan) 32,118 22,380 17,018 651 85 Private units 5,375 5,450 4,000 96 0 TOTAL 82,707 83,088 48,912 1,895 340 1 Covered area refers to irrigable land with irrigation infrastructure 2 Cultivated area includes some areas with more than one crop per year 3 Average exchange rate for that period was N$ 3.5 per US$ 1 Source: National Water Commission (CNA), Irrigation Districts Headquarters, Mixquiahuala, Hidalgo, Mexico, 1995 Table VII.2 Agricultural productivity in the Mezquital Valley, 1990-92 (t ha -1 a -1 ) Crops National mean Mezquital mean Hidalgo State irrigation area Rainfed area Sweet corn 3.7 5.1 3.6 1.1 Kidney bean 1.4 1.8 1.3 0.49 Oat 4.7 3.7 3.6 1.7 Barley (fodder) 10.8 22.0 15.5 13.5 Lucerne 66.3 95.5 78.8 0.0 Sources: Agricultural and Hydraulic Resources Secretary (SARH), Mexico 1994 (National values) National Water Commission (CNA), Irrigation Districts Headquarters, Mixquiahuala, Hgo., Mexico 1995 (Mezquital Valley data) The wastewater is contaminated with pathogenic organisms and toxic chemicals that constitute a health risk for both farmers and consumers of agricultural products. The principal crops grown are alfalfa, maize, wheat, oats, beans, tomatoes, chillies and beetroot. There is a small but valuable production of restricted crops in the lower section of the Valley (District 100), including lettuce, cabbage, coriander, radish, carrot, spinach and parsley. This crop restriction is part of the management policy for reuse of wastewater with adequate health safeguards. During its use in the Mezquital Valley irrigation districts, the Mexico City wastewater (a mixture of domestic and industrial waste) receives natural "land" treatment which is equivalent or superior to conventional secondary wastewater treatment. The environmental effects that could be experienced due to the water pollution that would result if this irrigation scheme was not available are: • The raw wastewater would lead to gross environmental pollution estimated at 1,150 t d - 1 organic matter, expressed in terms of their biochemical oxygen demand (BOD), which would affect the land and water resources downstream in the Panuco River basin, including several coastal lagoons and the Gulf of Mexico. • Municipal and rural water supplies, hydroelectric plants, fishery developments, aquatic ecosystems and a rich biodiversity would be affected. • Nutrient rich wastewater flowing downstream to the river basin would cause excess aquatic weed and vector infestation as a result of eutrophication. • The aesthetic value of the natural environment and the landscape would be affected by foaming and other effects, such as odour. • Without this huge, natural land treatment process it would be almost impossible to accomplish and to integrate sustainable development of land and water resources in a very important region of Mexico. VII.3 Pre-intervention situation At present, there are legal and institutional guidelines that ensure sustainable agricultural development in the Mezquital Valley. The National Water Law, in force since 1993, has one section dedicated specifically to the prevention and control of water contamination. In addition, Ecological Technical Standards 32 and 33 (now Official Mexican Standards) set down the requirements for wastewater use in agricultural irrigation (Diario Oficial de la Federacion, 1993). The National Water Commission (Comisión Nacional del Agua; CNA) was officially created in 1989 as a federal government entity responsible for promoting construction of the hydro-agricultural infrastructure, as well as for its operation, and for ensuring that the laws and standards relating to efficient use of water and control of its quality are upheld. The Federal Government, specifically CNA, has been in charge of the irrigation districts since 1949. Each district is under the administration of a chief engineer appointed by CNA, and being under the control of a single authority greatly facilitates management of the irrigation scheme. There is also a management board composed of representatives of central and state governments, water users associations and local credit banks. Some farmers work in co-operatives managed by themselves, although most are individual workers who own very small parcels of land (an average of 1.5 ha per user). Farmers lodge their water demands with the local District Office, specifying where and when the water is required. The District Manager then prepares a first draft of the irrigation schedule, analysing the different factors involved, such as the amount of water available, water demand timetables, the crop preferences of the farmers, agricultural authority policies, crop restrictions and resources available. The resultant irrigation programme (plan de riego) is implemented following discussion with, and approval by, the farmers who will take part in it. A fee is charged to the users (farmers) by CNA to recover some of the operational costs, although government subsidies remain high. Efforts are being made to eliminate these subsidies. The real operational and maintenance costs are around N$ 4.42 (4.42 new pesos) per thousand cubic meters and the farmers are paying only N$ 1.46 (33 per cent), plus N$ 0.75 (17 per cent) estimated as labour costs for small maintenance works (the average exchange rate for the 1993-94 agricultural cycle was N$ 3.5 per US$ 1). Therefore only 50 per cent of the operational costs are covered by the farmers using the wastewater. Every year since the beginning of this century, the government has provided funding for continuous extension of the irrigation infrastructure. It is rather difficult to estimate these construction costs as a component of the wastewater economic value because insufficient information is available. However, the farmers profits are often about 60 per cent from marketed crops and some salad vegetables can be more profitable (70 per cent and even 80 per cent). In the last four years, due to the spread of cholera, CNA has enforced restriction on crops irrigated with wastewater and whose products are consumed uncooked, such as salad crops. This decision, taken as a preventative measure, caused social conflict with farmers who saw their income severely reduced by the restriction of their cash crops without other viable alternatives being proposed. The volume of wastewater generated has increased over time. It is distributed in the Mezquital Valley by a complex system of tunnels, reservoirs and canals, which themselves have a purifying effect on the wastewater. The result is that different areas are irrigated with water of different quality. For example, at the entrance to the Valley, the wastewater has a maximum of 6 × 10 8 faecal coliforms per 100 ml, whereas at the outflow from the Vicente Aguirre reservoir the count is reduced to a minimum of 2 × 10 1 (Table VII.3). The same reduction occurs with helminths; the concentration of Ascaris eggs is reduced from 135 per litre at the Valley entrance to less than one per litre at the outflow of the lowest reservoir (Cortés, 1989; Cifuentes et al., 1994). This situation has stimulated the interest of academic institutions, which carry out epidemiological studies in the Mezquital Valley. Their first results (Figure VII.3) demonstrated that there is a higher risk of Ascaris lumbricoides infection in the infants of farm workers using raw wastewater than for those using partially treated wastewater from storage reservoirs, and that the risks for both groups were considerably higher than for those in the rain-fed control area. By contrast, the risk to children and adults in the reservoirs group was similar to that observed in the controls (rain-fed area). As expected, the age group 5-14 years, especially males, had the highest intensity of Ascaris infections when exposed to raw wastewater (Cifuentes et al., 1995; Blumenthal et al., 1996). In addition, these studies suggested an association between the prevalence of diarrhoeal disease and the exposure of the farmers' children to wastewater of different quality; children from households exposed to raw wastewater had a small but significantly increased risk. The higher rates of diarrhoeal diseases found in infants (1-4 years old), who mostly depend on their mothers, could be explained by crowded households, deficient hygiene practices and unsanitary conditions in the farmers' domestic environment (Figure VII.4) (Ordóñez, 1995). These results support the view that parasite infection is more effective as an indicator of the effects of wastewater use on the health of an exposed population. Table VII.3 Faecal coliform concentrations in the Mezquital Valley reservoirs (MPN 1 per 100 ml) Reservoir Geographic mean 2 Maximum 3 Minimum 3 Endho Inflow 2.6 × 10 7 6 × 10 8 3 × 10 4 Effluent 6.1 × 10 4 3 × 10 6 4 × 10 4 Rojo Gomez Inflow 5.3 × 10 5 3 × 10 4 5 × 10 3 Effluent 1.4 × 10 4 2 × 10 5 1 × 10 1 V. Aguirre Inflow 5.9 × 10 3 1 × 10 4 1 × 10 2 Effluent 3.3 × 10 2 3 × 10 4 2 × 10 1 1 Most probable number 2 Source: Cortés, 1989 3 Source: Cifuentes et al., 1995 Figure VII.3 Percentage Ascaris lumbricoides infection in different age groups of children according to the method of irrigation used for agriculture (After Cifuentes et al., 1994) Figure VII.4 Percentage of diarrhoeal disease in different age groups of children according to the method of irrigation used for agriculture (After Cifuentes et al., 1994) VII.4 Intervention scenario In 1993, Mexico hosted a regional workshop to analyse the issues surrounding agricultural wastewater use and to propose appropriate interventions to ensure public and occupational health and safety. The workshop was organised by the Mexican Institute for Water Technology (IMTA), with the assistance of the World Health Organization (WHO), the Pan-American Health Organization (PAHO), the Food and Agriculture Organization of the United Nations (FAO), the United Nations Environment Programme (UNEP) and the United Nations Centre for Human Settlements (UNCHS/HABITAT). Representatives from 12 countries in Latin America and the Caribbean participated. The workshop recommended the creation of a study and reference centre in the Mezquital Valley with the aim of promoting, co-ordinating and integrating investigative studies carried out in the favourable conditions found in that area. With regard to wastewater treatment as a measure for the protection of health and the environment, CNA is conducting detailed engineering studies in relation to the possible construction of conventional treatment plants in the Great Drainage Canal, in the metropolitan area of Mexico City, and in the discharge point from the Central Deep Outfall (Emisor Central) in the Mezquital Valley. In this respect, CNA has existing experience with treatment plants, both large and small, currently operating in the metropolitan area and whose effluents are used to irrigate green areas and to fill recreational lakes in the urban area. On a smaller scale, it may be possible to convince farmers to invest in treatment plants at the plot level to ensure safe production of salad vegetables and other high risk crops. At present, CNA is concentrating on assisting the farmers who use wastewater to build their own stabilisation ponds, to adapt the quality of the wastewater to the requirements for cropping restrictions and to demonstrate that the practices being used are safe. To ensure that these safe practices are used correctly, a strict wastewater quality certification programme is needed. Two events in the politics and administration of the country have facilitated more direct intervention in the future to improve the conditions under which wastewater is used in the Mezquital Valley. First, recent changes in the organisation of federal public administration, have placed the overall management of water (i.e. through CNA) under the newly created Ministry of Environment, Natural Resources and Fisheries. This will allow more emphasis to be given to environmental problems, which are precisely the central issue in the Mezquital Valley and which could affect downstream water resources in the Panuco River basin (as mentioned above). The second important event was the proposal to create the regional study centre in the Mezquital Valley. The specific objective of this centre is to enhance technical and scientific understanding in order to enable rational and safe use of waste-water and thereby to assist the development of sustainable agriculture. In order to assist the many and varied investigations in the Mezquital Valley, the reference centre should provide two basic facilities: • An information system including data generated by the field studies and environmental monitoring network. • Various demonstration units of an experimental and educational nature, to facilitate training and technology transfer. VII.5 Lessons learned, constraints and opportunities The project to create a study centre in the Mezquital Valley faces obstacles commonly found in developing countries. These are: • High levels of poverty and unemployment which are aggravated by excessive demographic growth, and a currency (the peso) weighed down by external debt and a shortage of financial resources. • Persistent conditions of environmental deterioration. Above all, the need for basic domestic sanitation in rural areas demands attention and competes for scarce funds. • Strong market pressure to adopt developed country solutions which are inappropriate (technically, economically and financially) for developing countries. The treatment of wastewater is a good example of this. • The process of administrative decentralisation. In its initial phase this results in serious difficulties with co-ordination, usually because there are few well-prepared professional and technical personnel available at the local level. Nevertheless, there are factors that favour the implementation of the project, such as: • Many institutions and researchers, both national and international, are interested in carrying out appropriate studies. • There is political will to halt environmental deterioration and to revert present trends in order to ensure sustainable development. • The basic institutional infrastructure exists to implement interventions for improving agricultural production and water sanitation in the irrigation districts. • Some international co-operation agencies are interested in giving technical and financial assistance to the proposed study centre, because of its regional relevance for countries in Latin America and the Caribbean. The InterAmerican Development Bank, for example, has indicated its interest in the project. The Bank, together with the Japanese government has approved a US$ 800 million credit for large-scale wastewater treatment plants in the metropolitan area of Mexico City, as well as for the necessary hydraulic infrastructure. VII.6 Conclusions and recommendations • The rational use of wastewater for irrigation in agriculture and forestry, or in aquaculture, is a highly useful and productive practice that contributes to sustainable development which is the central objective of Agenda 21 as approved at the United Nations Conference on Environment and Development (UNCED) in Rio de Janeiro in 1992. • The interventions necessary to improve the efficiency of wastewater use, in order to protect health and safeguard the environment, require a full understanding of local socio- cultural and economic conditions. Such understanding must result in action, which should be translated into guidelines and applied promptly. • In the Mezquital Valley, irrigation conditions are ideal for carrying out field research. The results of this research could be used at the national level and eventually in other developing countries. Taking the above points into account, it is proposed: • To support the creation of a Regional Study and Reference Centre for the rational and safe use of wastewater in the Mezquital Valley. • To enforce crop restrictions and other wastewater use regulations, based on recent epidemiological findings. • To introduce simultaneously a pilot intervention programme of basic housing sanitation in the irrigation area. VII.7 References Blumenthal, U.J., Mara, D.D., Ayres, R.M., Cifuentes, E., Peasey, A., Scott, R., Lee, D.F. and Ruiz Palacios, G. 1996 Evaluation of the WHO nematode egg guideline for restricted and unrestricted irrigation. Wat. Sci. Tech. 33(10-11), 277-83. Cifuentes, E., Blumenthal, U.J., Ruiz-Palacios, G., Bennett, S. and Peasey, A. 1994 Escenario epidemiológico del uso agrícola del agua residual: el Valle del Mezquital, México. Salud Públ. Méx., 36(1), 3-9. Cifuentes, E., Blumenthal, U.J., Ruiz-Palacios, G. 1995 Riego Agrícola con Aguas Residuales y sus Efectos sobre la Salud en México, del libro Agua, Salud y Derechos Humanos. Iván Restrepo. México. CNA 1995 Información proporcionada por la Jefatura de los Distritos de Riego del Valle del Mezquital. Comisión Nacional del Agua, Mixquiahuala, Hidalgo, México. Cortés, J. 1989 Caracterización Microbiológica de las Aguas Residuales con Fines Agrícolas. Informe del estudio realizado en el Valle del Mezquital. Mexican Institute of Water Technology (IMTA), Jiutepec, México. Diario Oficial de la Federacion 1993 NOM-CCA-032-ECOL/1993 and NOM-CCA-033- ECOL/1993. México, 18 Octubre 1993. INEGI 1994 Sistemas de Cuentas Nacionales de México. Instituto Nacional de Estadística, Geografía e Informática (INEGA), Mexico. Ordoñez, B.R. 1995 Personal communication, Mexico. Romero, A. H. 1994 Estudio de Caso (Valle del Mezquital). In: Proceedings Taller Regional para las Américas sobre Aspectos de Salud, Agricultura y Ambiente, Vinculados al Uso de Aguas Residuales. Mexican Institute of Water Technology (IMTA), Jiutepec, México, SARH 1994 Anuario de la Producción Agrícola. Ministry of Agricultural and Hydraulic Resources, México, D.F., Mexico. EMARNAP 1996 Programa Hidráulico 1995-2000. Secretaria de Medio Ambiente, Recursos Naturales y Pesca (SEMARNAP), Mexico. Water Pollution Control - A Guide to the Use of Water Quality Management Principles Edited by Richard Helmer and Ivanildo Hespanhol Published on behalf of the United Nations Environment Programme, the Water Supply & Sanitation Collaborative Council and the World Health Organization by E. & F. Spon © 1997 WHO/UNEP ISBN 0 419 22910 8 Case Study VIII* - Lerma-Chapala Basin, Mexico * This case study was prepared by José Eduardo Mestre Rodríguez VIII.1 Introduction In many of its regions, Mexico currently faces an imbalance between water demand and availability, primarily due to natural water scarcity as well as uneven water quality distribution. Rapid urban and industrial growth, among other economic and social factors, have made this worse. Water needs have grown, water users are fiercely competing with each other and conflicts are emerging as a result. Water quality has also deteriorated as urban and industrial effluents are often discharged with no previous treatment. Furthermore, Mexico is slowly overcoming a severe economic and financial crisis which has limited hydraulic infrastructure development and impoverished large population sectors. Mexico covers 1.97 million km 2 of the North American continent (Figure VIII.1), with a population of 91.12 million growing at 1.8 per cent a year. Politically, Mexico is divided into 31 autonomous states (each one with its own elected government) and a federal district, which includes Mexico City. A complex system of mountain ranges create 310 hydrological basins which experience different degrees of hydraulic development and water pollution. Of all the Mexican basins, Lerma-Chapala is the most important. Consequently, it receives priority attention at all three government levels, federal, state and municipal, and especially from the National Water Commission (Comisión Nacional del Agua; CNA) which is the sole federal authority entrusted with overall national water resources administration. Public awareness on water issues in Lerma-Chapala has led to the active participation of water users, non-governmental organisations (NGOs) and social institutions with a plethora of interests directly or indirectly linked with the water sector. Figure VIII.1 Location map showing the position of Mexico and the Lerma-Chapala basin VIII.2 The Lerma-Chapala basin The River Lerma with a length of 750 km originates in Mexico's central high plateau at an altitude above 3,000 meters above sea level (masl). The river ends in Lake Chapala (1,510 masl) which is the largest tropical lake in Mexico (Figure VIII.2), 77 km long and 23 km wide. The maximum storage capacity of the lake is 8.13 km 3 and the surface area is about 110,000 ha. The lake is also rather shallow; its average depth is 7.2 m, with a maximum of just 16m. The Lerma River basin, is a tropical region with an average temperature of 21 °C, an area of 54,400 km 2 (less than 3 per cent of Mexico's entire territory) and an average rainfall of 735 mm a -1 , mainly concentrated in the summer, from which a mean run-off of 5.19 km 3 is derived. The River Santiago arises from Lake Chapala and flows westwards finally reaching the Pacific Ocean. The Santiago River basin is less developed in terms of population and economic activity, except for Guadalajara, the second largest city in Mexico, and with a metropolitan area with more than 3.5 million inhabitants. Some 26,000 deep water wells operate within the Lerma-Chapala basin, with very low efficiency rates, due to their high electricity consumption and rather low water yields. Almost 70 per cent of all 38 aquifers in the region are overexploited (Figure VIII.3). [...]... or groundwater borders) were finally, and legally, recognised as the ideal geographical unit for rational water management The National Water Act could perhaps have gone further with its definition of Basin Councils because, for all practical purposes, the Consejo de Cuenca Lerma-Chapala was already further advanced than was required by law For the first time in Mexican history, the Water Act included... National Water Act (December, 1992), inspired by the Consulting Council process, enforced the creation of basin councils throughout the country to improve institutional co-ordination and to enhance all forms of fruitful relationships amongst users and water institutions The water act assigned CNA a key role in regional water management within the federal government Furthermore, it encouraged greater... offer user-friendly systems Regional water sector statistics are now being offered either in a printed form, following a similar pattern to the French Water Information Network (Réseau National des Données sur l'Eau) managed by the International Office for Water (Office International de l'Eau) in Limoges, France, or on CD-ROM, through proprietary procedures provided by the Mexican Institute for Water Technology... providing a reasonable water service for irrigation, for industry and for households Furthermore, such a situation fostered the limited participation of water users and generated a negative attitude towards water resources management and supply Even today, when changes are currently being implemented, many users (at all levels and sectors) are still reluctant to pay for water Potable water supply had reached... uncommon at all levels including disputes for water among neighbouring states In general, water quality had fallen to a new, unacceptably low level In specific locations, water quality had deteriorated so badly that life itself, in all its forms and manifestations, was challenged River basin protection was almost non-existent Erosion had increased in former forest areas and grasslands were disappearing... eventually attracted water users Hence, within the Consulting Council, a Water Users' Assembly was created as a powerful body that could listen to a plethora of water demands, as well as provide a swift vehicle for raising to the Council level the needs, hopes and means of water users for contributing to the improvement of the hydraulic situation in the LermaChapala Basin Eventually, water users' representatives... water abstraction VIII.3 Pre-intervention situation Before 1989, the regulatory and legal framework provided clear procedures for surface run-off measurement and the related information systems and analysis tools; but there were serious deficiencies in water quality monitoring and recording In addition, institutional structures, mostly centralised at the federal level, were unable to slow down water quality... surface run-off uses (mainly for irrigation and potable water supplies), combined with the general discharge of untreated effluents, have given rise to serious regional, and local, pollution problems Frequent conflicts over water quality occur in Chapala Lake which plays a key role as the main water source for Guadalajara Figure VIII.3 Aquifers in the Lerma-Chapala basin indicating their level of water. .. scheme were rather complex given that, for example, sewage systems were incomplete in several cases and billing procedures were underdeveloped in some other sites Before the Clean Water Program was enacted in April 1991, potable water was mainly disinfected using chlorine On a regional basis 5,763 l s-1 were disinfected water, equivalent to 31 per cent of the total water supply, to service 2.2 million... treatment Federal Government-owned electrical and petroleum industries in the basin have also built large-scale treatment plants to purify and reuse their wastewater; their overall capacity is 415 1 s-1 The second stage of the Lerma-Chapala clean-up programme, which is already under way, aims to increase treatment capacity to 10,670 1 s-1 of municipal and industrial wastewater by means of constructing . as the main water source for Guadalajara. Figure VIII.3 Aquifers in the Lerma-Chapala basin indicating their level of water abstraction VIII.3 Pre-intervention situation Before 1989, the. for rational water management. The National Water Act could perhaps have gone further with its definition of Basin Councils because, for all practical purposes, the Consejo de Cuenca Lerma-Chapala. Informe del estudio realizado en el Valle del Mezquital. Mexican Institute of Water Technology (IMTA), Jiutepec, México. Diario Oficial de la Federacion 1993 NOM-CCA-032-ECOL/1993 and NOM-CCA-03 3- ECOL/1993.