Water resources management is a significant challenge for Mexico. The country has in place a system of water resources management that includes both central (federal) and decentralized (basin and local) institutions. Furthermore, water management is imposing a heavy cost to the economy.
The arid northwest and central regions contain 77% of Mexico's population and generate 87% of the gross domestic product (GDP).CONAGUA. Estadísticas del Agua en México, Edición 2008 By contrast, the poorer southern regions have abundant water resources. Surface and groundwater resources are overall overexploited and polluted thus leading to an insufficient water availability to support economic development and environmental sustainability. These challenges are expected to become more complicated as climate change creates more extreme weather and further heat and dry weather in already arid regions.
Water management history and recent developments
Mexico has a long and well-established tradition on water resources management (WRM) which started approximately in the 1930s when the country began investing heavily in water storage facilities and groundwater development to expand irrigation and supply water to the rapidly increasing population.
The 1934 Código Agrario, promulgated during the Cárdenas administration (1934–1940), granted the federal government powers to define the "public interest" to which water could be harnessed. By virtue of such legislation, between the 1930s and 1970s, the rural community and ejido sector were subject to direct federal control over water. Private landowners, on the other hand, enjoyed the benefits of federally subsidized irrigation infrastructure and guaranteed market prices. Over time, large landowners became highly capitalized, while small land owners, by the 1970s, were suffering from the effects of water monopolies.
In the 1970s, the Mexican government entered into a tripartite agreement with the World Bank and the United Nations Development Programme to prepare the 1975 National Water Plan (NWP), which identified the need to enact a New Water Law (NWL) and a National Water Authority (ANA) as well as decentralize responsibilities and promote water user participation in operational and maintenance (O&M). The NWP spurred a significant institutional development and infrastructural achievements: (i) the federal government transfer responsibilities for water supply and sanitation to municipalities and states in 1983, (ii) the Mexican Institute of Water Technology was established in 1986, (iii) the National Commission on Water (CONAGUA) was established in 1988, and (iv) in 1989, the first Basin Council was created in Lerma Chapala, incorporating water users from multiple sectors.
During the 1990s, there was expedited groundwater development and aquifer pumping for combined agricultural, urban, and industrial demand. In addition, the federal government decentralized responsibility for maintaining large irrigation infrastructure to autonomous agencies (irrigation districts).
In 1992, Mexico adopted the Ley de Aguas Nacionales (LAN), which contained specific provisions for the role of the CONAGUA, the structure and functioning of river basin councils, public participation in water management, etc. In 1993 the Cutzamala system, one of the largest pumping schemes in the world, was completed. The Cutzamala system pumps of water into the Mexico City metropolitan area.
In 1997 the first technical groundwater committee was created to manage an overexploited aquifer in the state of Guanajuato.
With the 2004 revision of the National Water Law, the thirteen decentralized CNA regions would become basin organizations serving as the technical arm of more broad-based basin councils that incorporate civil society interests including the private sector and citizens' groups.
Water resource base
Surface and ground water resources
Mexico's internal renewable water resources per capita is , which is below the average in the Central American and the Caribbean region, .
Total internal renewable water resources are 457 billion cubic meters (BCM)/year, plus 49 BCM/year inflows from neighboring countries (average 1977–2001).World Resources Institute Mexico and World Resources Institute Water A total of 65% of this surface runoff occurs in seven rivers: Grijalva, Usumacinta, Papaloapan, Coatzacoalcos, Balsas, Panuco, Santiago and Tonala, whose total watershed area represents 22% of the country's total land area. The Balsas and Santiago rivers empty on the Pacific Ocean, while the other five empty into the Gulf of Mexico. The largest river on the Pacific coast is the Balsas River (24 BCM/year) and the largest river on the Atlantic Coast is the Grijalva–Usumacinta flowing from Guatemala to Mexico (115 BCM.year). The longest river (2018 km) and also the river with the largest basin (226,000 km2) is the Rio Bravo, called Rio Grande in the United States.
The historical mean annual precipitation (1941–2004) is , with 77% of all precipitation accruing between June and October. Rainfall is highly variable and droughts are frequent. The states most affected by drought, as measured by the agricultural area affected by drought, are Chihuahua, Mexico and Zacatecas.CNA 2006, p. 45 A little over 70% of rainwater in Mexico is lost through evapotranspiration and returns to the atmosphere. The rest runs off rivers and streams or infiltrates into the subsoil and recharges groundwater.
Mexico shares three watersheds (Colorado, Bravo and Tijuana) with the United States, four with Guatemala (Grijalva, Usumacinta, Suchiate, Coatan, and Candelaria) and one with Belize and Guatemala (Rio Hondo). The waters are shared with the U.S. in accordance with the stipulations included in the Treaty relating to the utilization of waters of the Colorado and Tijuana Rivers and of the Rio Grande, signed in 1944.
Groundwater accounts for 64% of the volume for public water supply, 33% of all water used for agriculture and livestock, and 24% of water utilized by self-supplied industry. There are 653 groundwater aquifers in Mexico. CONAGUA estimates the total amount of groundwater recharge to be around per year, 36.4% of which, (around per year) are actually used. This average rate does not fully represent the situation of the arid region, where a negative balance is threatening the sustainable use of groundwater resources.
Groundwater is a key water supplier for several users in the arid region or in some cities where groundwater is most of the time the sole water resource available. About 71% of the groundwater is used for agriculture, 20% for water urban supply and 3% for domestic and animal use.
Water is abundant in the relatively sparsely populated South and scarce in the more densely populated Center and North of the country. The Center and the North of the country where 77% of Mexico's population lives and 85% of its GDP is generated dispose of only 32% of the country's renewable water resources.CNA 2006, p. 38
Storage capacity and infrastructure There are 667 large dams with a storage capacity of 150 BCM and an actual storage of 70 BCM in 2005.CNA 2006, p. 88 Mexico has 4,000 dams and other hydraulic infrastructure with a storage capacity of , which account for 44% of the annual flow. In the arid regions, dams are mostly used for irrigation. In the humid areas, dams are mostly used for electricity generation. Dams are also considered a means for flood protection in Mexico. Approximately 63 dams have a storage capacity of over , and account for 95% of Mexico's storage capacity. The largest reservoirs are La Angostura (20,217 km2), Nezahualcóyotl (14,0298 km2), Chicoasén (11,883 km2), and Infiernillo (11,860 km2).Centro Virtual de Información del Agua.
There are seven major lakes in Mexico. By far the largest and most important is Chapala Lake between the states of Jalisco and Michoacán with an area of 1,116 km2 and a storage capacity of . Actual storage volume varies between 1 and 10 BCM since measurements began in 1935.CNA 2006, p. 51 The lake is only 4 to 6 m deep. Mexico has approximately 70 lakes with a storage capacity of .
Main lakes and storage capacityLakeRiver basin areaStorage capacityFederal Entitykm2sq mihm3acre feet Chapala Jalisco and Michoacan Cuitzeo Michoacan Patzcuaro Michoacan Yuriria Guanajuato Catemaco Veracruz Tequesquitengo Morelos Nabor Carrillo Mexico Source: CONAGUA
Water quality According to the Water Quality Index, 96% of Mexico's surface water bodies have different levels of pollution. OECD estimates the economic cost of water pollution in Mexico at US$6 billion per year. The problem is most serious in the Valle de Mexico region where 100% of the water bodies have different levels of contamination, 18% of which are highly polluted. Low water quality is due to untreated discharge of industrial effluents and municipal wastewater into rivers and lakes, solid waste deposits along river banks, uncontrolled seepage from unsanitary landfills, and non-point pollution mainly from agricultural production.
CONAGUA has also detected infiltration of untreated municipal wastewater in 8 aquifers, iron and manganese in 2, arsenic in 1 aquifer of the Lagunera region. In overexploited aquifers, contamination tends to worsen over time as the groundwater reservoir is depleted. This is the case of the Lagunera region, where concentration of 0.09 to 0.59 mg/L of arsenic found in the drinking water, are above of the permissible level of 0.05 mg/L. In addition, information regarding water quality, available by the Public Water Rights and Registry, is scarce and often unreliable.
Information on the water quality of Mexico's rivers published by the National Water Commission is limited to only two parameters, Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD). No other water quality indicators are used to classify water bodies and no water quality data using other pollutants as parameters are readily available.
Surface water bodies in Mexico are classified in five different ambient water quality classes, using BOD and COD as indicators.CNA Pollution Classification In 2005 surface water quality was measured in 509 sites using these parameters.
Using BOD as an indicator, in 2005 5% of water bodies were classified as highly contaminated (BOC > 120 mg/L) and 10% as contaminated.(BOD > 30 mg/L). If COD is used as an indicator, the respective shares increase to 12% for highly contaminated (COD > 200) and 26% for contaminated (COD > 40) waterbodies.CNA Pollution Map
The highest levels of contamination are found in the hydrological regions of the Northeast, Balsas, Valley of Mexico and Lerma-Chapala.CNA 2006, p. 60
Water resources management by sector Total water withdrawals for consumptive use are 78 BCM/year. The largest consumptive water user is agriculture (78%), followed by domestic use (17%) and industry (5%). There are no estimates on the Minimum Environmental Flow Requirements in Mexico. Environmental demand thus is de facto absent from the official water balances in Mexico.
Overall, only 18% of water resources in Mexico are withdrawn for consumptive use. However, there is water stress in several regions of the country. The highest pressure on water resources is encountered around Mexico City (120% of resources), in Baja California (86% of resources) and in Sonora in the Northwest (79% of resources).
CNA has defined 653 "aquifers" out of which 104 were categorized as overexploited in 2005.CNA 2006, p. 52 Total groundwater use was 27.5 BCM/year, while recharge is estimated at 77BCM/year. Out of the country's 13 administrative hydrological regions, in 4 regions abstraction exceeds recharge: Baja California, Northeast, North-Center and the Valley of Mexico.
Water withdrawal per sector in 2005Withdrawal Freshwater Groundwater Total %hm3acre feethm3acre feethm3acre feet Agriculture (a) 76.8 Domestic 14.0 Industrial (b) 9.3 Total 100Source: CONAGUA