The removal of nitrate from aqueous solutions of a synthetic medium and groundwater was examined using various aquatic plants, such as water hyacinth, water lettuce and salvinia. Water hyacinth reduced the nitrate level to 64% in a synthetic medium containing 100 mg l(-1) of nitrate. The efficiency of nitrate removal was further increased to 80 and 83% with initial nitrate concentrations of 200 and 300 mg l(-1), respectively, but was decreased with 400 and 500 mg l(-1). This was due to osmotic pressure at higher concentrations not supporting the uptake of nitrate. Water lettuce and salvinia showed lower nitrate removal efficiencies in the same medium. In the groundwater samples, the nitrate removal was greatly dependent upon the presence of other nutrients, such as sulphate and phosphate, which caused lower nitrate uptake by water hyacinth. The quality of the physico-chemical parameters in the groundwater samples were found to be low in water treated with water hyacinth compared to untreated water.