Water resources management in Mexico

Watersheds of Mexico. Basins in green drain to the Pacific, in brown to the Gulf of Mexico, and in yellow to the Caribbean Sea. Grey indicates interior basins that do not drain to the sea.

Mexico's internal renewable water resources per capita is 4,016 cubic metres (141,800 cu ft), which is below the average in the Central American and the Caribbean region, 6,645 cubic metres (234,700 cu ft).

Total internal renewable water resources are 457 billion cubic meters (BCM)/year, plus 49 BCM/year inflows from neighboring countries (average 1977–2001).[4] 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.[5] 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 773 mm (30.4 in), with 77% of all precipitation accruing between June and October.[6] 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.[7] 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.[8]

Mexico shares three watersheds (Colorado, Bravo and Tijuana) with the United States, four with Guatemala (Grijalva, Usumacintam 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 on the utilization of the waters of the Colorado, Tijuana and Rio Grande Rivers, 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 77 cubic kilometres (18 cu mi) per year, 36.4% of which, (around 28 km³ or 6.7 cu mi 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.[9]

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.[10]

There are 667 large dams with a storage capacity of 150 BCM and an actual storage of 70 BCM in 2005.[11] Mexico counts with 4,000 dams and other hydraulic infrastructure with a storage capacity of 180 cubic kilometres (43 cu mi), 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 100,000,000 cubic metres (81,000 acre⋅ft), and account for 95% of Mexico's storage capacity.[8] The largest reservoirs are La Angostura (20,217 km²), Nezahualcóyotl (14,0298 km²), Chicoasén (11,883 km²), and Infiernillo (11,860 km²).[12]

There are seven major lakes in Mexico. By far the largest and most important is the Chapala Lake in Central Mexico with an area of 1,116 km² and a storage capacity of 8,126 cubic hectometres (1.950 cu mi). Actual storage volume varies between 1 and 10 BCM since measurements began in 1935.[13] The lake is only 4 to 6 m deep. Mexico has approximately 70 lakes with a storage capacity of 14 km³ (3.4 cu mi).

Source: CONAGUA

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.[14]

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.[14]

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.[15] 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.[16]

The highest levels of contamination are found in the hydrological regions of the Northeast, Balsas, Valley of Mexico and Lerma-Chapala.[17]

In 1998, domestic consumption accounted for 17% of surface water withdrawals in Mexico. During the past decade, the Mexican water supply and sanitation sector made major strides in service coverage. In urban areas almost 100% of the population is estimated to have access to improved water supply and 91% to adequate sanitation. In rural areas, the respective shares are 87% for water and 41% for sanitation.[19] Coverage levels are particularly low in the southern regions. (See also Water supply and sanitation in Mexico)

In 1998, agriculture accounted for 78% of surface water withdrawals in Mexico. A total of 62,000 km² (15.3 million acre) count with irrigation infrastructure (22.9% of the total cultivated area), 55,000 km² (13.6 million acres) of which are actually irrigated. In 1997, 58,000 km² (14.3 million acres) use surface irrigation, 3,000 km² use sprinkler irrigation and 1,000 km² localized irrigation. Ineffective irrigation has generated salinization and drainage problems in 3,841.63 square kilometers (949,290 acres) of a total irrigated area of 62,560 square kilometers (15,460,000 acres).[8] (See also Irrigation in Mexico)

The electricity sector in Mexico relies heavily on thermal sources (74% of total installed capacity), followed by hydropower generation (22%) in 2005.[20] The largest hydro plant in Mexico is the 2,300 MW Manuel Moreno Torres in Chicoasén, Chiapas. This is the world's fourth most productive hydroelectric plant.[21]

A Lepisosteus, one of the endemic species of Mexico

There are approximately 70 lakes in Mexico, covering a total area of 3,700 square kilometers (910,000 acres). Some of these lakes, especially in the eastern side, have a volcanic origin and count with numerous endemic species. Lake Chapala, the largest Mexican lake, is considered a hydrological priority region for biodiversity conservation due to its 39 local species, 19 of which are endemic. The Lake Catemaco, located in Veracruz, has 12 native species 9 of which are endemic.[22]

Wetlands in Mexico are dynamic, complex and productive ecosystems. Six major wetland are registered in the Ramsar Convention on Wetlands: Lagartos River (Yucatan Peninsula), Cuatrocienagas (Coahuila), La Encrucijada (Chiapas), Marsh Nayarit and Sinaloa, Centla Swamp (Tabasco), and the Colorado River (Baja California).

Cenotes, sinkholes on the Yucatan peninsula that are filled with groundwater, host a number of unique species from bacteria, algae and protozoa (i.e. copepoda, cladocera and rotifera) to vertebrates (i.e.lepisosteus).[22] Cenotes are the main water source for many ancient and contemporary Maya people, as there are no rivers and very few lakes on the peninsula.

The main law governing water resources management in Mexico is the National Water Law of 1992 (Ley de Aguas Nacionales -LAN), revised on April 29, 2004.[23][24]

According to the LAN key functions in the sector are the responsibility of the federal government, through the National Water Commission (CNA or CONAGUA). CNA's mission is to "manage and preserve national water resources, with the participation of the society, to reach a sustainable use of the resource." CNA has a staff of 16,000 and an annual budget of 18.6 billion pesos in 2005 (more than US$1.5bn) and is considered to be one of the most powerful federal agencies in Mexico. CNA administrates major federal programs to support investments in water supply and sanitation as well as in irrigation. It also directly manages certain key hydraulic facilities such as the Cutzamala Pipeline that supplies a large share of the water used in the Metropolitan Area of Mexico City. CNA also owns and operates most dams in Mexico and operates the country's water monitoring network. The LAN made possible to implement a regulatory framework that seeks to encourage greater efficiency and a more accurate perception of the social, economic, and environmental value of water resources. Therefore, waters users operate within a framework of rights and obligations that are clearly defined in three basic instruments:

• Titles of concession or allocation, which establish the right to withdraw, use or enjoy in usufruct a specific volume of water
• Permits for wastewater discharges. This instrument establishes the concession under which permittees must dispose of resulting wastewater
• Enrollment in the Public Registry of the Water Rights (Registro Público de Derechos de Agua – REDPA) of both titles of concession or allocation and permits for discharging wastewater, which affords the rights granted to water users greater certainty and assistance from a legal standpoint.

The 2004 amended National Water Law (NWL) aims to restructure CONAGUA key functions through the transfer of responsibilities from the central level to subnational entities: the basin agencies (Organismos de Cuenca – BA) and Basin Councils (Consejos de Cuenca – BC). BA and BCs are expected to play an increasing role in the sector limiting CONAGUA's role to the administration of the NWL, the conduct of national water policy, and planning, supervision, support and regulatory activities.

The NWL also introduced a Water Financing System (Sistema Finaciero del Agua – SFA). CONAGUA will create together with the Ministry of Finance appropriate instruments to determine funding sources, spending guidelines, cost recovery, settling of accounts and management indicators.

Through the 2004 revision of the National Water Law two new entities were formally created: Basin Councils (Consejos de Cuenca) and Basin Agencies (Organismos de Cuenca). The basin councils consist of representatives of the federal government, state and municipal governments, as well as at least 50% representatives of water users and NGOs. The basin councils are not decision-making bodies, but are consultative bodies. There are 26 basin councils. The basin agencies, on the other hand, are the regional administrative branches of the CNA, which retains the ultimate decision-making power.

Obviously other entities such as the Ministry of Finance, the Federal Congress, State Governments and State Congresses, as well as the Ministry of Environment and Natural Resources are important decision-makers in the sector.

Three groups of institutions have been assigned with the main responsibilities for WRM: (i) the National Water Commission (Comisión Nacional del Agua –CONAGUA), at the federal level; (ii) Water Commissions (Comisiones Estatales del Agua – CEAs), at the State level; and (iii) basin authorities and basin councils.

CONAGUA is the highest institution for water resource management in Mexico, including water policy, water rights, planning, irrigation and drainage development, water demand management, water supply and sanitation, and emergency and disaster management (with an emphasis on flooding). CONAGUA's mission is to manage and preserve national water resources, with the participation of the society, to reach a sustainable use of the resource.

CONAGUA is formally under the authority of the Ministry of Environment and Natural Resources (Secretaria del Medio Ambiente y Recursos Naturales – SEMARNAT) but it enjoys considerable de facto autonomy. It employs 17,000 professionals, has 13 regional offices and 32 state offices and had an annual budget of US$1.2 billion in 2005. It also directly manages certain key hydraulic facilities such as the Cutzamala Pipeline that supplies a large share of the water used in the Metropolitan Area of Mexico City. CONAGUA also owns and operates most dams in Mexico and operates the country's water monitoring network.[14]

The CEAs are autonomous entities that usually are under the authority of the State Ministry of Public Works. Their attributions are different among states and can include water resources management, irrigation and the provision of water supply and sanitation services.

The recently created Basin Authorities (BAs) will develop from the 13 existing Regional Offices of CONAGUA and are expected to be responsible for formulating regional policy, designing programs to implement such policies, conducting studies to estimate the value of the financial resources generated within their boundaries (water user fees and service fees), recommending specific rates for water user fees and collecting them. Basin Councils (BCs) are expected to guide, together with CONAGUA, BAs work. There are a total of 25 BCs that have been established with the same basin boundaries as the BAs.[14] Some states are located entirely within the area of one BC. In other cases, one state is divided between two or more BCs. In the latter case, the state participates in all of the BCs within its territory.

The 2004 amended National Water Law (NWL) aims to restructure CONAGUA key functions through the transfer of responsibilities from the central level to subnational entities: the basin agencies (Organismos de Cuenca – BA) and Basin Councils (Consejos de Cuenca – BC). BA and BCs are expected to play an increasing role in the sector limiting CONAGUA's role to the administration of the NWL, the conduct of national water policy, and planning, supervision, support and regulatory activities.

The NWL also introduced a Water Financing System (Sistema Finaciero del Agua – SFA). CONAGUA will create together with the Ministry of Finance appropriate instruments to determine funding sources, spending guidelines, cost recovery, settling of accounts and management indicators.

The National Water Plan 2007-2012, linked to the National Development Plan, aims at ensuring water quality and quantity, recognizing the strategic value of water and promoting sustainable water use and water resources conservation. The Plan has eight objectives, namely: (i) increasing agricultural productivity, (ii) increasing access and quality of water supply and sanitation services, (iii) promoting integrated water resources management at the river basin level, (iv) improving technical, administrative and financial development of the water sector, (v) increase participation of water users and society in general in the management of water resources, (vi) reduce water risks, (vii) evaluate climate change impacts on water resources, and (viii) promote compliance with the National Water Law, especially on administrative matters.

Each objective has a strategy and a set of goals associated. The NWP has a total budget of 227,130 million pesos (about US$21.9 billion), which does not include operational and maintenance costs of hydraulic infrastructure.