Duckweeds are monocotyledonous aquatic plants having ability to rapid vegetative reproduction to form genetically uniform clones. In this study, duckweeds (Lemna minor) are used for the study of laboratory scale in the reduction of parameters such as BOD, COD, nitrate, nitrite, ammonia, TSS, sulphate, phosphate and chloride under different detention time (10, 12, 15, 20 and 30 days). Reduction values of these parameters were increased with corresponding increase in detention time. Hence duckweed can be used as model system for the study of water pollutants and an alternative choice for the study of some toxic chemicals present in the pollutants.