Reverse Osmosis (RO) and Nanofiltration (NF) are techniques for separation of molecules with a low molecule weight from solvents, mostly water.
It based on separation of solute material by the membrane because of size and load. In contrast to ultrafiltration (UF) membranes are RO and NF Membranes able to separate the most salts and unloaded solute materials. NF and RO belong to the membrane filtration technologies. Compare to microfiltration and ultrafiltration are NF and RO membranes not porous. The separation effect does not only depend on size of the particles also on their affinity to the semipermeable membrane. That means that the separation depends on size and load. The membranes are no absolute barrier. RO and NF are used to separate solute from water.