Water purification is process of removing contaminants including pesticides from water. As hazardous substances, pesticides are very difficult to be removed from aquatic media. Recently, nanofiltration membranes have emerged extensively as a promising process due to their economical attractiveness which can effectively eliminate organic material and pesticides. In this book, fabrication and modification procedure of different nanofiltration membranes by various polymers and modifiers are discussed, and their morphology, characterization and performance in removal of nitroaromatic pesticides are investigated under different operating conditions and in the presence of natural organic matter. Retention of compounds is strongly influenced by solution pH, physicochemical properties of solutes, and characteristics of the membranes, etc. Retention of neutral solutes is dominated by steric exclusion, while electrostatic charge repulsion and adsorption govern the retention of charged contaminants. This book represents the complexities of filtration of nitroaromatic compounds, the effects of different parameters on separation process, and a basis for treatment of surface waters.