In Algeria, wastewater, too often discharged without appropriate treatment, is the main source of degradation of water quality, both surface and groundwater. Agriculture, in its turn, participates in this degradation by the exaggerated use of pesticides and chemical fertilizers. The objective of this work is to evaluate the quality of water in the Mitidja plain through the monitoring of various physico-chemical parameters. Globally, the mineralization of water is acquired by dissolution of geological formations and evaporation of the water table with a more or less important influence of the marine invasion in the eastern Mitidja. Anthropic processes, mainly related to the irrational use of chemical fertilizers in agriculture are also attributable. The hydrochemical mapping showed a zonality of chemical elements concentrations with an elevation of salinity in the extreme east and west of the plain. The water from the boreholes located in the western and central part of the aquifer is of good chemical quality, which gradually deteriorates as it moves eastwards across the plain.