Do Nanofiltration Systems Soften Water?

You might be surprised to learn that even something seemingly innocuous as water can contain all sorts of impurities, from minerals to bacteria. For us to use water, it is essential to eradicate these impurities and that’s where nanofiltration systems come in. But do they also have the power to soften water? This piece attempts to answer this question.

Figure 1 Nanofiltration system.


Nanofiltration identifies as a membrane-based filtration technology that expels organic compounds, dissolved minerals, and dissolved solids from water. The pore size of an NF membrane falls between that of a microfiltration (MF) membrane and a reverse osmosis (RO) membrane, being smaller than the former and more significant than the latter.

Nanofiltration employs polymer materials in producing membranes that feature pore sizes within the 1-10 nanometer range, which are characteristically very small.

Figure 2 Nanofiltration process.

Do Nanofiltration Systems Remove Hardness?

Water with high levels of dissolved minerals can cause scaling and buildup in equipment that comes into contact with it, such as pipes and appliances. This can lead to decreased efficiency and increased maintenance costs. The minerals must be removed by softening the water to prevent these issues. Nanofiltration systems are capable of achieving this to some degree.

They can selectively remove hardness minerals while retaining other beneficial minerals and ions in the water. These systems are commonly utilized in industrial and residential settings for treating hard water. However, the effectiveness of nanofiltration in softening hard water relies on the specific composition of the water and the membrane employed in the filtration process.

Softwater vs hardwater

How Does Nanofiltration Soften Water?

Nanofiltration is a widely used technique for reducing the hardness of water because it can selectively eliminate the ions that cause water hardness.

● Pretreatment

Before introducing water into the nanofiltration system, it is usually treated beforehand to remove any substantial impurities or contaminants that could harm the membrane. This pre-treatment may entail filtering the water through media such as carbon, sand, or other substances, as well as chemical treatment to modify the pH or oxidize impurities.

● Nanofiltration

The hard water is then pushed through a nanofiltration membrane with small pores measuring just a few nanometers. These pores allow water molecules to pass while blocking larger ions and molecules. The membrane can be created from various materials such as ceramic or polyamide.

● Softened Water Collection

The water that flows through the nanofiltration membrane is now softened and can be collected for usage. Softened water generally has lower levels of calcium and magnesium ions, which reduce the formation of scale on appliances and other fixtures.

Benefits of Using Nanofiltration Systems to Eliminate Hardness

Nanofiltration systems.

When used for water softening, nanofiltration systems can offer several benefits over traditional ion exchange methods:

  • More selective: Nanofiltration membranes can selectively remove divalent ions (such as calcium and magnesium) from the water while leaving monovalent ions (such as sodium) largely untouched. This means that nanofiltration can soften water without adding excess sodium to the water, which can be a concern for people on low-sodium diets.
  • Lower waste production: Ion exchange systems produce a large amount of waste brine, which can be difficult and expensive to dispose of properly. Nanofiltration systems produce less waste, making them a more environmentally friendly option.
  • Smaller footprint: Nanofiltration systems typically require less space than ion exchange systems, which can be beneficial for applications where space is limited.
  • Lower maintenance requirements: Nanofiltration systems require less maintenance than ion exchange systems, which can translate to fewer downtime periods and lower maintenance costs over time.
  • Reduced chemical usage: Unlike other water softening methods such as ion exchange, nanofiltration does not require the use of chemicals such as salt or acids. This means that there is less environmental impact and lower operating costs associated with chemical procurement and disposal.

Figure 3 Ion exchange water softener.

Nanofiltration Softeners Vs Ion Exchange Softeners.

Although both nanofiltration (NF) softeners and ion exchange (IE) softeners are effective in water softening, they vary in several aspects.

Working Principles:

  • As mentioned earlier, nanofiltration softeners eradicate hardness by trapping calcium and magnesium minerals using a semi-permeable membrane.
  • Ion exchange softeners, on the other hand, rely on charged resin beads to swap divalent ions for sodium ions, consequently softening the water. The principle behind the exchange process involves ion exchange, whereby ions with the same charge are swapped between the resin and the water.

Impurity Removal Range:

  • Nanofiltration softeners are efficient in eliminating divalent ions like calcium, magnesium, and certain larger organic molecules. Yet, they are less capable of filtering monovalent ions such as sodium and chloride, which have smaller sizes than divalent ions.
  • On the other hand, ion exchange softeners are highly proficient in eliminating divalent ions like calcium and magnesium. However, they have limitations in removing other contaminants such as viruses, bacteria, and organic compounds.

Impurity Removal Range.


  • Compared to ion exchange softeners, nanofiltration softeners tend to be pricier due to the costly semi-permeable membranes and higher energy demands for system operation.
  • On the other hand, ion exchange softeners are relatively economical among various water treatment systems, as their cost primarily reflects the expense of resin beads and energy needed for resin regeneration.

Maintenance Practices:

  • Regular maintenance is necessary for nanofiltration softeners, as the semi-permeable membranes need to be cleaned and replaced as required.
  • Similarly, periodic regeneration is required for ion exchange softeners to rejuvenate the resin beads.

The frequency of maintenance and regeneration for the former and later depends on the water quality and the amount of water being processed.

Nanofiltration softeners.


  • Nanofiltration softeners take up less space than ion exchange softeners, as they don’t necessitate significantly huge resin beds and regeneration tanks.
  • On the other hand, ion exchange softeners occupy more space than nanofiltration systems due to their requirement for large resin beds and regeneration tanks.
Scroll to Top