What Is The Deionisation Process?

At ReAgent, we sell deionised water by the 1,000L bucket-load – but what is deionisation exactly?

Quite simply, deionisation is a process by which water has 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?

Key Takeaways

• Deionised water is created by removing all charged ions

• Cation and anion resins exchange ions for H⁺ and OH⁻, forming pure H₂O

• Low electrical conductivity confirms successful deionisation

• DI water is used in vehicles, electronics, cooling systems, and perfumes

The Basics Of Deionisation

Deionisation (DI) is a method used to strip water of its mineral content and dissolved salts, leaving an exceptionally pure liquid. 

Unlike ordinary filtration or boiling, DI focuses specifically on removing electrically charged particles, which are often responsible for scaling, corrosion, or interference in sensitive processes.

The process uses specialised resin beads that capture and hold ions from the water. These beads are engineered to target either positive or negative charges, ensuring that every type of mineral or salt is eliminated. 

Over time, the beads can be refreshed with safe chemical water treatments, restoring their ability to purify water repeatedly.

This level of refinement makes deionised water suitable for a variety of demanding uses, from precise laboratory experiments to industrial cooling systems where ordinary tap water would fall short. 

By reducing mineral content to nearly zero, deionised water provides a clean, neutral medium that won’t react with delicate components or equipment.

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 two 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.

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.

How Can You Tell Deionisation Has Worked?

Ions conduct electricity. This means that we are able to measure the ionic content of the water by running an electrical current through it  in a process known as electrical conductivity.

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 successful.

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.

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

BLOODHOUND SSC Project

One of the examples above is a key element in the the record-breaking BLOODHOUND Project, who have been carrying out test runs in front of the public.

Reaching 210 mph, the supersonic car only gave a taste of what it’s going to be capable of. BLOODHOUND now progresses 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.

Conclusion

From high-speed adventures and microelectronics, to cooling systems and perfume, deionised water has a plethora of usages. It’s more than just purified water, but instead is a vital component for precision, performance, and safety. With nearly 50 years of experience, ReAgent ensures that every drop meets high purity standards, helping you achieve results you can trust.