ABSTRACT
In most semi-arid zones of Mexico groundwater is the main source for potable, agricultural and industrial use. At present, the study area, San Luis Potosi (SLP) City (figure 1) is one of the conurbations of Mexico with the highest annual growth rate (5-7%) with about 9,00,000 inhabitants. In the last 30 years, some 95% of its total water supply for human consumption has been obtained from groundwater. Prevailing semi-arid conditions make natural water resources limited, such that waste-water reuse for irrigation purposes makes a lot of sense. However, irrigation with untreated waste-water can cause deterioration of shallow groundwater quality, further limiting available water resources for potable use. Shallow
groundwater was used for drinking water purposes in the study area until some 100 years ago. As the drainage basin is naturally closed, waste-water produced by inhabitants has drained to the parts with lowest elevation and has usually been consumed in the nearby district of Soledad de Graciano Sanchez (SGS) for crop irrigation. In 1995 an estimated discharge of about 1.9 m3s1 of waste-water (95% urban domestic and commercial and 5% urban industrial) was used for the irrigation of over 2200 ha (CNA, 1995). In 2001 the city obtained its groundwater supply (about 3.0 m3s1) from more than 120 boreholes tapping a deep aquifer located below the shallow aquifer.
