What is Deionisation?

Lucy Bell-Young

by Lucy Bell-Young

9th November 2017

At ReAgent, we sell deionised water by the 25L bucket-load – but what is deionisation exactly? 

Quite simply, it is water that has had its ions removed in order to form pure H20. Ions are electrically charged atoms or molecules that have either a positive or negative charge. For many applications, water containing ions is considered impure and cannot be used until these impurities have been removed. So how does deionisation happen?

Ion Exchange

Deionisation (DI) occurs when water passes through a mixed ion exchange bed where both positively and negatively charged resins are used to remove their respective ions. Ion exchange resins are used to facilitate this process, and can be categorised into 2 groups: cations and anions.

Cations are positively charged atoms or molecules, such as Calcium (C++) and Magnesium (Mg++), and can be removed from water by cation resin. Anions, on the other hand, have a negative charge. Sulphates (SO4–) and Nitrates (NO3-) are examples of anions found in water that are similarly removed by anion resin.

Resins are made from organic polymer chains that form small, plastic beads. These are porous, and have a diameter of about 0.6mm. The charged functional groups that make up these resin beads are what attract particular ions before they are replaced.

Since ions conduct electricity, it is important to maintain electrical neutrality throughout this process. This means that each ion that is attracted into the resin bead must be replaced by an ion that is leaving the resin bead. This is what is called ion exchange.

Resin beads used in deionisation

“Resins are made from organic polymer chains that form small, plastic beads. These are porous, and have a diameter of about 0.6mm. “

Cation Resin

Since cations are positively charged, cation resin has a negative functional group in order to attract the positive ions present in the water. Before this process can begin, cation resin must first be regenerated with Hydrochloric Acid (HCl).

The acid is used to rinse other cations from the resin. These are then replaced with the positively charged Hydrogen (H+), which attaches to the negatively charged cation resin bead, replacing the positive atoms or molecules that have been removed.

Anion Resin

In a similar fashion, anion resin has a positive functional group in order to attract negatively charged anions in the water. Sodium Hydroxide (NaOH) is used instead of Hydrochloric Acid for the regeneration of anion exchange.

Just as cations are exchanged for Hydrogen (H+) as they pass through the resin beads, anions are exchanged for Hydroxyl (OH-). When all cations and anions have been removed from the water, the hydrogen and hydroxyl combine to form pure H20. This is when the water has become completely deionised.

 But How Can You Tell Deionisation Has Worked?

As we mentioned earlier, ions conduct electricity. This means that we are able to measure the ionic content of the water by running an electrical current through it. Since ions in water are used as stepping stones for electricity, the less ions that are present the lower the conductivity.

In pure H20 no ions are available to carry the charge through the water. Therefore, if there is a low or non-existent conductivity value in the water, we know that deionisation has been succesful.

With almost 50 years of industry experience and first class customer service, ReAgent goes one step further than deionisation to provide you with Ultrapure water, which you can order here. 

To see our deionisation and water purification process in action, watch the video below!


Not blown away by the potential of deionised water yet? You will be when we tell you that ReAgent are a proud sponsored supplier of DI water to the record-breaking BLOODHOUND SSC Project, who carried out their first test run in front of the public last month.

Reaching 210 mph, the SuperSonic Car only gave a taste of what it’s going to be capable of. BLOODHOUND now progress towards breaking the land speed record by travelling at 1000 mph. Since regular fuel is likely to corrode the engine, ReAgent are supplying BLOODHOUND with quality deionised water. This means that, because all minerals have been removed, it won’t damage or contaminate the engine, helping the SuperSonic Car reach its full potential.

Read more about how ReAgent’s supply of DI water has impacted this mind-blowing project.

Testing deionised water in BLOODHOUND engine component

Just a glimpse into the components that go into the BLOODHOUND SuperSonic Car! Photo taken at the workshop we attended.

From high-speed adventures and microelectronics, to cooling systems and perfume, deionised water has a plethora of usages which you can read all about in one of our earlier blog posts.

Want to get in on this miracle elixir? Thanks to ReAgent, it’s now at your fingertips. From 25L containers to bulk tankers, we have you covered on every front. Simply click here to order your deionised water today!


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