Surface and Ground Water Resources
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).
A volume of 396 cubic kilometres (95 cu mi) of water per year flows through Mexico's rivers, including imports from other countries and excluding exports. 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 historical mean annual precipitation (1941–2004) is 773 mm (30.4 in), with 77% of all precipitation accruing between June and October. 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.
Read more about this topic: Water Resources Management In Mexico, Water Resource Base
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