Distilled Water vs Demineralised Water: What's the Difference?

When shopping for purified water in Australia, you will encounter various terms including distilled water, demineralised water, deionised water, and purified water. While these products may appear similar on store shelves, significant differences exist in how they are produced and what applications they best suit. Understanding these distinctions helps you choose the right product for your specific needs.

The Distillation Process Explained

Distilled water is produced through a physical process that mimics nature's own water cycle. Water is heated until it becomes steam, leaving behind minerals, bacteria, and most contaminants. This steam is then cooled and condensed back into liquid form, resulting in highly purified water.

The distillation process effectively removes nearly all impurities from water. Minerals like calcium and magnesium, which cause hardness in tap water, are completely eliminated. Bacteria and viruses cannot survive the heating process. Even many organic compounds and heavy metals are left behind when the water vapourises.

The purity of distilled water is typically measured at 99.9% or higher. This means that less than 0.1% of the original contaminants remain in the final product. For most household and medical applications, this level of purity exceeds requirements.

One limitation of distillation is that some volatile organic compounds with boiling points similar to water may carry over with the steam. However, quality distillation processes include additional steps to minimise this concern.

How Demineralised Water is Produced

Demineralised water, sometimes called deionised or demin water, uses chemical or electrical processes to remove mineral ions from water. The most common method involves passing water through specially designed resin beads that attract and capture mineral ions through an ion exchange process.

In ion exchange demineralisation, water flows through columns containing positively charged cation resin and negatively charged anion resin. The cation resin captures minerals like calcium, magnesium, and sodium, replacing them with hydrogen ions. The anion resin captures chloride, sulphate, and nitrate ions, replacing them with hydroxide ions. The hydrogen and hydroxide ions combine to form pure water molecules.

Reverse osmosis is another method used to produce demineralised water. This process forces water through a semi-permeable membrane that blocks most dissolved solids while allowing water molecules to pass through. Reverse osmosis can remove up to 99% of dissolved minerals.

The key distinction is that demineralisation specifically targets mineral ions. While effective at removing minerals, these processes may not remove all types of contaminants as thoroughly as distillation. Bacteria, viruses, and some organic compounds may pass through demineralisation systems if additional treatment steps are not included.

Comparing Purity Levels and Applications

Both distilled and demineralised water achieve high purity levels, but the types of impurities removed differ. For applications where mineral content is the primary concern, demineralised water may be perfectly adequate. However, when broader purity is required, distilled water offers more comprehensive purification.

For CPAP machines and other medical equipment, distilled water is generally recommended. The complete removal of both minerals and microorganisms provides the cleanest possible water for breathing therapy. Our product comparison tool helps you find medical-grade distilled water suitable for these sensitive applications.

Automotive applications like battery top-ups and radiator coolant mixing work well with either product. The primary requirement is mineral-free water that will not cause scale buildup or interfere with chemical processes. Many Australian automotive stores stock demineralised water specifically for these purposes.

Laboratory and scientific applications often specify which type of water is required. Some experiments need ultrapure distilled water to ensure no interference from any contaminants. Others may require only demineralised water when mineral-free conditions are sufficient.

Steam irons and humidifiers can use either distilled or demineralised water effectively. Both prevent the mineral buildup that causes white residue and clogs spray nozzles. The choice often comes down to availability and price in your local area.

Price and Availability Considerations

In Australia, demineralised water is often slightly less expensive than distilled water. This reflects the lower energy costs of ion exchange processes compared to the heating required for distillation. However, prices vary significantly between brands and retail outlets.

Supermarkets typically stock both products, though selection varies by location. Demineralised water is commonly found in the cleaning products aisle, while distilled water may be located with pharmaceutical supplies or in automotive sections.

For bulk purchases, automotive supply stores often offer the best value on larger containers of demineralised water. Medical supply stores and pharmacies may have better selection for distilled water, particularly products designed for CPAP and other medical applications.

Online retailers including Amazon Australia provide convenient access to both product types with home delivery. Comparing prices across multiple sources often reveals significant savings, especially for regular users who purchase larger quantities.

Making the Right Choice for Your Needs

When deciding between distilled and demineralised water, consider your specific application requirements. If manufacturer specifications call for distilled water, using demineralised water may not provide the same level of performance or protection.

For most household applications where mineral-free water is the goal, both products deliver satisfactory results. The practical differences in everyday use are minimal, and either choice helps protect your appliances from scale buildup and mineral damage.

Medical applications warrant more careful consideration. CPAP machines, nebulisers, and other breathing equipment benefit from the comprehensive purification provided by distillation. The additional cost is modest compared to the value of protecting both your equipment and your health.

If you are unsure which product suits your needs, check the manufacturer's recommendations for your specific equipment. Most user manuals clearly state water requirements. When in doubt, distilled water is the safer choice, as it meets or exceeds requirements for virtually all applications.

Storage requirements are similar for both products. Keep containers tightly sealed and store away from direct sunlight. Use opened containers within a reasonable timeframe to maintain purity, and never return unused water to the original container after pouring.