This manuscript studies the problem of the wastewater influence on groundwater chemistry, particularly the microbiological quality setting and risk to public health in an urban environment, in an arid climate. The study of the spatial and temporal variation in the chemical and microbiological composition of Béchar city groundwater identifies the impact intensity that directly affects its quality. Microbiological analysis (total bacteria, total coliforms, Streptococcus, Clostridium sulphite-reducing), including microorganisms research (fecal coliform) indicators of anthropogenic pollution (sewage) is also made, confirmed and interpreted by significant microbial load presence, the highest ones are located south of the city. The evaluation of the risk index for the determiner: groundwater ingestion, with Pb and Zn ions, for children and adults, is significant, and worth 1.3 (Pb, children) which expresses a public health real risk presence, and appropriate measures must be recommended to eliminate it.
Key words: Béchar, quality, groundwater, microbiology, waste water, risk index.