The watershed of the aquifer in Toluca Valley is located in the upper reaches of the Lerma River in the federal state of Mexico and covers 23 municipalities with about 2 million inhabitants and 10 industrial zones on an area of 2,738 km². Due to excessive groundwater extraction in Toluca Valley, in particular for potable water (about 80% of extraction, 60% thereof for Mexico City), the groundwater level has dropped sharply and continues to decline by more than 1 m a year on average.
Deforestation of the main percolation areas on the mountain slopes and the shift in land use have raised surface runoff, which causes pronounced erosion and impairs natural groundwater replenishment, thus aggravating the situation. Furthermore, untreated wastewater and uncontrolled dumping of refuse pollutes surface water and groundwater