page_title: Water resources management in Mexico
section_title: Surface and ground water resources
hierarchical_section_title: Water resources management in Mexico / Water resource base / Surface and ground water resources
caption_attribution_description: English: Section of the map "Watersheds", from the US Department of Interior's National Atlas of the United States
context_page_description: Water resources management is a significant challenge for Mexico. 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. By contrast, the poorer southern regions have abundant water resources;however, surface and groundwater are overexploited and polluted thus leading to an insufficient water availability to support economic development and environmental sustainability. The country has in place a system of water resources management that includes both central and decentralized institutions.
context_section_description: 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). 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 773 mm (30.4 in), 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. 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, 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.
  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.
caption: 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.
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