In order to assess the purification efficiency of infiltration basins as used in France for wastewater treatment of small municipalities, infiltration on sand columns was studied. The efficiency of the infiltration was assessed by studying the physico-chemical and microbiological characteristics of the treated water. In all four sands the total suspended solids were totally eliminated. The removal of chemical oxygen demand was substantial as long as aerobic conditions were maintained. Aerobic conditions disappeared after approximately one week in fine sands because of clogging. Nitrification occurred in the coarse sands only. However nitrification was not complete. No significant degree of denitrification was observed. Phosphorus retention was high during a preliminary period of a few days. Because of their fast clogging the use of the finest sands for effluent treatment is not advisable. For disinfection purposes the thickness of sand beds and not only the granulometry should be considered. (from English summary)