Conserving water resources and protecting them from the pollution are of high importance in natural cycle of our life. Nitrate, as one of the important sources of water pollution, is a serious threat to aquatic ecosystems, and due to its high solubility, its extraction from the water is a costly process. Providing a reliable, low cost and fast method is necessary for eliminating pollution. This study tried to determine the refining potential and capacity of Eichhornia crassipes for removing nitrate from the water. Factors such as initial concentration of nitrate, contact time, absorbent mass, pH and the presence of other competing ions such as sulfate on nitrate absorption have been studied. The results showed that the best efficiency of nitrate removal, more than 99%, in the optimum condition (the retention time of 30 hours, absorbent dose three plants (15 stems) and pH = 6.4) occurred. In addition, the efficiency of nitrate removal in the presence of sulfate ions did not reduce. By increasing the initial nitrate concentration, from 30 to 150 mg/L, there was no significant change in removal efficiency. Actually, by increasing absorbent mass, removal time increased from 67.96% to 100%. The process of nitrate absorption followed Langmuir isotherm (R-2 = 1). However, the results showed that Eichhornia crassipes, a promising plant with great functionality, can be used as a refiner for removing nitrate and it is a simple, efficient and low cost method.