Nanofiltration is a membrane filtration process that operates between ultrafiltration and reverse osmosis. It uses membranes with pore sizes typically ranging from 1 to 10 nanometers, allowing it to selectively remove small particles, organic molecules, and divalent ions while letting monovalent ions pass through. This makes it useful for water treatment, food processing, and pharmaceutical applications. The technology is effective in softening water by removing hardness ions like calcium and magnesium, while retaining beneficial minerals. Nanofiltration is also employed in various industries to concentrate solutions, recover valuable materials, and improve product quality, making it a versatile tool in modern filtration systems.