What is the difference between reverse osmosis and nanofiltration?

Nanofiltration is a membrane method for liquid separation between reverse osmosis and ultrafiltration. Reverse osmosis can remove the smallest solute with molecular weight less than 0.0001 micron, and nanofiltration can remove the solute with molecular weight around 0.001 micron. In essence, nanofiltration is a kind of low pressure reverse osmosis, which is suitable for the treatment of well water and surface water when the purity of produced water is not particularly strict. Nanofiltration is suitable for water treatment systems that do not need to have high desalination rates like reverse osmosis, but have a high ability to remove hardness components, sometimes called "softening membrane". The nanofiltration system has low operating pressure and lower energy consumption than the corresponding reverse osmosis system.