The Basin of the Valley of Mexico is a closed basin of 9600 km(2), where average annual precipitation (1980-55) is 746 mm (226.7 m(3)/s). Calculated actual evapotranspiration, is 72-79% of the precipitation. The surrounding mountain ranges of the Sierra de Las Cruces, Sierra Nevada, and Sierra Chichinautzin are the main recharge areas for the enclosed Basin, in decreasing order, Calculated recharge rate is a maximum of 19 m(3)/s in the Metropolitan Zone,:whereas a recent estimate of the groundwater exploitation rate indicates that 51.35 m(3)/s is being withdrawn from the Basin aquifer systems, resulting in a deficit of more than 30 m(3)/s. Taking into account infiltration processes by leaking water-supply systems, the calculated deficit is reduced to 20.5 m(3)/s. Overexploitation of the natural aquifer systems is also indicated by an average annual decline of Im of the potentiometric levels of the shallow groundwater systems. Possible solutions include: (1) the use of surface runoff water (unused amount in 1995:17.6 m(3)/s) for consumption purposes, which is currently pumped to areas outside the Basin; (2) an increased number and capacity of treatment plants; (3) the renovation of the leaky water-distribution network; (4) the reinjection of treated water, and (5) possible exploitation of deep regional aquifer systems.
