It might seem odd to think that the clear, odourless liquid on which we depend as humans can come in so many different forms, yet that is indeed the case. But what are the differences between them? Here, we look at the difference between distilled water and deionised water.
Distilled water and deionised water are both forms of purified water, but to understand the difference between them, we first need to understand exactly what they both are.
In this post:
Key Takeaways
- Distilled water removes both minerals and most bacteria/viruses through boiling and condensation
- Deionised water removes mineral ions but not biological contaminants, using ion exchange resins
- Distilled water can be used in steam irons, CPAP machines, car batteries, laboratory experiments, sterilising medical tools, and brewing
- Deionised water often seen used in cleaning industrial equipment, window cleaning, cooling systems, and cosmetics
What is Distilled Water?
Distilled water, as the name suggests, is water which has had its impurities removed via a process called distillation. This is a process that has been used for more than 2,000 years when our ancestors distilled sea water to create something more potable.
Distilled water is used as a cooling agent in car engines, in laboratory experiments, to clean medical tools, make soap, in canned fruit and veg, and in brewing beer, amongst many other things.
The Distillation Process
In this process, water is boiled and the steam created is condensed into a clean, sterilised container. While scaled to larger devices at the industrial scale, this is a common scientific experiment in schools and laboratories, illustrated below:
The distillation process removes salts, along with most minerals and other impurities, leaving solid contaminants behind. The condensed liquid at the other end is distilled water. While very pure, it can be purified further through double distillation and further processes.
What is Deionised Water?
Deionised (or demineralised) water is a purified water that has had almost all of its mineral ions removed, such as sodium, calcium, iron, and chloride. The deionisation process does not, however, remove most bacteria or viruses.
Uses of deionised water include as a cooling agent in medical devices, in cleaning industrial machinery, in some aquariums and in cosmetics.
Distilled and deionised water are in many cases interchangeable, although distilled (or double distilled) water should be used if an extremely pure form of water is needed.
The Deionisation Process
To begin the deionisation process, water is passed through resin beads that carry an electrical charge. There are two types of resins used: One positively charged and one negatively charged.
As the water flows through, these resins work by swapping the unwanted mineral ions in the water for hydrogen (H⁺) and hydroxide (OH⁻) ions.
Once the ion exchange is complete, the hydrogen and hydroxide ions rejoin together to form pure water (H₂O). The result is deionised water, a highly purified form of water that is free from charged contaminants.
What is the Difference between Distilled Water and Deionised Water?
Distilled and deionised water are both forms of purified water. The main difference is that in distilled water, most bacteria and viruses have been removed while some minerals are left behind.
The deionisation process, in contrast, completely removes minerals from the water but doesn’t remove most bacteria or viruses.
Distilled water is normally more expensive than deionised water as the production process takes longer, especially on an industrial scale. Deionisation is much quicker and more efficient, and therefore deionised water is cheaper. It is therefore more commonly used when distilled water isn’t essential.
Can you Drink Distilled or Deionised Water?
Some people do prefer to drink distilled water, but it lacks the minerals found in both tap and spring water and these minerals have both health and taste benefits.
However, deionised water should not be consumed as its “highly aggressive” properties mean it can cause adverse health effects, according to the World Health Organisation.
In addition, deionised water could still contain bacteria and viruses, which are not things you generally want to put in your body. It’s better used in machinery, fish tanks, and in other industrial applications.
Applications Of Distilled and Deionised Water
While both types of purified water serve a similar purpose, their different methods of purification mean they are better suited to specific applications.
Laboratory and Industrial Uses
In laboratory and industrial environments, the level of water purity required depends on the task at hand. Distilled water is often used in settings where microorganisms, bacteria, or viruses could interfere with results or processes. This includes certain chemical experiments, the preparation of reagents, and the sterilisation of medical instruments.
Deionised water, on the other hand, is typically used when the focus is on eliminating mineral ions that could cause scaling, corrosion, or chemical interference. It is commonly used in electronics manufacturing, pharmaceutical production, cleaning sensitive equipment, and in cooling systems where mineral build-up could be problematic.
In ultra-sensitive scenarios such as in high-precision laboratory testing or in semiconductor manufacturing, distilled water may still be favoured due to its broader contaminant removal of other electronic chemicals.
Household and Everyday Applications
Both distilled and deionised water can be found in household products and appliances, though usually not for drinking.
Distilled water is frequently used in steam irons, humidifiers, CPAP machines, and car batteries, where mineral deposits could clog or damage the equipment over time. It’s also used in the dilution of certain cleaning products or beauty treatments.
Deionised water is more commonly found in window cleaning solutions, automotive cooling systems, and home aquariums when appropriately re-mineralised. It’s valued for being free from minerals that might leave behind spots or residues, making it ideal for surface cleaning and rinsing.
Conclusion
Distilled and deionised water may appear identical, but their differences lie in the purification process and the types of impurities removed. Distilled water is better for applications where biological contaminants are a concern, while deionised water is ideal for environments where mineral content must be eliminated. Ultimately, choosing the right type of purified water depends on your specific needs, be it for laboratory precision, industrial efficiency, or everyday appliance longevity.
