Nano filtration uses a series of thin-film membrane elements engineered for use with fouling-prone brackish water applications. Normally nano filters is designed to utilize an three-layer membrane, of which a proprietry middle layer creates extreme smoothness. Good quality membrane are superior than standard polyamide spiral wound membrane elements for desalination of difficult feed water sources. High quality membranes enables lower fouling, reduced overall energy usage, increased membrane service life and an extension of operating time between required cleanings, which in turn reduce expenditures on required chemicals.Good quality elements provides high rejection of divalent and multivalent anions while monovalent ion rejection is dependent upon feed concentration and composition.These type of membrances consist of family of thin film ultrafiltration membrance elements which are chearaterized by a molecular weight cutoff of 8000 on polyethylene glyol and a smooth fouling resistant membrance surface. These ultrafiltration elements are used for RO pretreatment, color, TOC reduction and colloidal iron and silica removal.Choosing a good quality membrane elements for municipal drinking water plants need to consider that it should provide a low pressure and cost effective nanofiltration alternative to standard RO treatment. The result product should be virtually free from any harmful biological matter. Performance is charaterized by hardness reduction, color removal, and orghanic pollutants reduction. Energy conversion and salt rejection performance is also very important considerations.