A water treatment system with a high desalination rate like reverse osmosis, but with a high ability to remove hardness components, is sometimes referred to as a "softened membrane" nanofiltration system with low operating pressure and lower energy consumption than the corresponding reverse osmosis system.
Nanofiltration is a membrane liquid separation technology located between reverse osmosis contract ultrafiltration. Reverse osmosis can remove solutes with a molecular weight of less than 0.0001 microns, and nanofiltration can remove solutes with a molecular weight of about 0.001 microns. Nanofiltration is essentially a low-pressure reverse osmosis, used in places where the purity of produced water is not particularly strict after disposal. Nanofiltration is suitable for disposal of well water and surface water. Nanofiltration is not necessary.