The Henaya Irrigated Perimeter (HIP) is an agricultural area irrigated by treated wastewater (TWW) of Ain El Hout treatment plant. Various analyses have shown that i) this water has low concentration of heavy metals and toxic elements, ii) the average values of the physicochemical parameters for 136 samples are satisfactory (29.2 mg O2∙dm−3 for chemical oxygen demands – COD, 13.14 mg O2∙dm−3 for biological oxygen demands – BOD, 14.2 mg∙dm−3 of suspended matter – SM, 1.82 mg∙dm−3 of N-NO3, 7.7 for pH and 927.74 μS∙cm−1 for electric conductivity – EC). Thirdly, it contains a high number of bacteria and nematodes (7200 CFU∙(100 dm3)−1 for faecal coliforms and 30 eggs∙dm−3 for intestinal Nematodes) which makes it dangerous for groundwater contamination.The objective in this work is to characterize the TWW and evaluate the impact of it use for irrigation on the quality of Hennaya groundwater. Before this, one has to prove that there is an amount of TWW that feeds the water table to show that there is a risk of pollution. We then estimated the aquifer minimum recharge value by TWW using the Thormthwaite method. The estimation has given 92 mm which is an important quantity. The results of the groundwater microbiological analyses reveal no sign of contamination. The cause is the efficiency of the degradation of pollutants of the Vadose zone. The soil purifying power Md of the HIP was evaluated by the Rehse method and gave values ranging from 2.1 to 12.7 which indicated a complete purification.

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