Reverse osmosis is a frequently used process in the field of water desalination. By reverse osmosis, monovalent ions can be removed from the water. This requires adequate diaphragms and high operating pressures up to 60 bar.

Nanofiltration (NF) is an identical process. However, the retention rates are lower than in reverse osmosis. Nanofiltration works with a lower water pressure of less than 8 bar. Nanofiltration or NF is therefore often referred to as low-pressure reverse osmosis (LPRO).

The main application of nanofiltration is the softening of drinking water, the removal of DOC (decolouration) or the retention of anthropogenic trace substances.

Nanofiltration removes solids while gases can diffuse through the membrane. This leads to the need for deacidification after softening with nanofiltration. This can be done e.g. by cross-flow aeration.