Distilled vs Deionized Water

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Wondering how to tell distilled water and deionized water apart?

In this guide, we’ve defined and discussed the differences between these two water types, including their method of water treatment, contaminants removed, uses, and costs.

πŸ“Œ Key Takeaways:

  • Distilled water is purified water that’s made in a water distiller.
  • Deionized water is demineralized water that’s made in a water deionizer.
  • Both water sources are similar, but they have differences in their production process, uses, contaminants removed, and costs.

πŸ†š What’s The Difference Between Distilled Water and Deionized Water?

The main difference between distilled water and deionized water is that distilled water is free from virtually all impurities, while deionized water is free from dissolved mineral salts and other particles, but still contains contaminants that aren’t electrically charged.

βš—οΈ What is Distilled Water?

Distilled water is demineralized water that’s completely pure.

To produce distilled water, a water distiller boils the water until it evaporates. Most impurities don’t have the same boiling point as water, so they’re left behind in the boiling chamber. Meanwhile, the vaporized water travels through a cooling chamber into a separate container, where it condenses back into liquid form.

Distilled water is free from virtually all contaminants, including heavy metals, chemicals, microorganisms, VOCs, and more.

Waterwise 4000 Water Distiller review
Water distiller

Pros And Cons Of Distilled Water

Here’s a quick overview of the pros and cons of the water distillation process:


  • All impurities removed
  • 100% safe to drink
  • Lacks minerals so won’t form scale
  • Various uses, including medicinal
  • Affordable & low-maintenance at-home water treatment


  • Has a “flat” or plain taste
  • May leach contaminants from containers & pipes due to its lack of impurities
  • Slightly acidic due to its lack of minerals
  • Very slow water purification process

🚰 What is Deionized Water?

Deionized water, as the name suggests, has had all its ions removed, resulting in a liquid that has no charge. Deionized water can be produced naturally in the environment, as well as in deionizers, which allow you to manually adjust water’s pH.

The process of producing deionized water involves sending water through ionically charged resins. When water comes into contact with the resin beads, the ions in the water are transferred into the resin, and are replaced with hydrogen and hydroxyl ions (to balance out the water’s charge). This is known as ion exchange.

Deionized water is free from ionic contaminants, including nearly all minerals, salts, carbon dioxide, and some organic contaminants.

Us water systems 3 stage DI system
DI system

Pros And Cons Of Deionized Water

Here’s a quick overview of the pros and cons of the water deionization process:


  • Highly pure and free from ions, minerals, and most impurities
  • No minerals so non-scale-forming
  • Suitable for various scientific, industrial, and medical applications.
  • Quick and easy to produce


  • At-home deionizing systems are more expensive
  • Lack of minerals affects taste & health properties of water
  • May leach metals from containers & pipes
  • Not guaranteed to be 100% contaminant-free

πŸ“ Main Differences Between Distilled And Deionized Water

Now we know what they are and how they’re made, let’s look at the main differences between deionized and distilled water:

Water Treatment Method

Distilled water is produced in a water distillation system, while deionized water is produced in a water deionizer.

Both of these are water purification systems, but they use different treatment methods to achieve slightly different results.

A distiller boils tap water until it evaporates, then transports the water vapor into a separate container, where it condenses. Most impurities can’t evaporate with boiling water, so they remain in the boiling chamber during the distillation process.

A deionizer sends water through charged resins, where ion exchange takes place. The charged ions in the water are replaced with ions that don’t affect water quality (usually hydrogen and hydroxyl ions). This produces demineralized water.

Deionization is a chemical process, while distillation is not. DI water is much faster to produce than distilled water – the deionization process takes just minutes, while a standard countertop distiller takes 4-6 hours to produce a single 1-gallon batch of pure water.

deionized water used in laboratory

Contaminants Removed

Distilled water is virtually free from all tap water contaminants and is classed as purified water. DI water is free from charged ions, but will still contain traces of chemicals and microorganisms (which the DI process can’t remove).

The distillation process removes the highest concentrations of impurities. Minerals, salts, chemicals, pathogens, metals, and virtually all other impurities apart from the water particles themselves can be removed when producing distilled water.

Distilled liquids aren’t completely free of impurities, however; VOCs and a few other select particulates have a higher boiling point and can evaporate and condense when water is distilled. Most water distillers have a post-activated carbon filter, which removes lingering contaminants from the water.

The deionized water produced by a deionizer is free from ions – i.e. inorganic charged particles. Only ions are removed, so chemicals like chlorine, volatile organic compounds, PFAS, microorganisms, and any other contaminants without a charge aren’t removed by the DI process alone.

Oftentimes, deionization is used alongside an additional water filtration process, like reverse osmosis. Reverse osmosis filters water thoroughly, eliminating or greatly removing the contaminants that might be left behind after deionization.


Both distilled and deionized tap water are free from minerals and salts, which means they’re often used interchangeably in applications that require a mineral-free water source.

DI is usually used in cooling applications, industrial processes, and manufacturing. At home, this type of water is used in fish tanks and car batteries. It’s also used for cleaning.

Distilled water is commonly used to sterilize medical equipment. It’s also used in the manufacturing of beauty products and in laboratory applications. At home, distilled tap water can be used for a number of household purposes, including topping up a steam iron or car cooling system, watering plants, or filling aquariums.

Both water types can be used as a drinking water source, and both are considered safe to drink. However, drinking water that has been treated with deionization or distillation has a “plain” taste and may leach certain metals and plastics due to its “hungry” status.

Pouring distilled water from glass container


Water distillers are usually at least half the price of deionization machines. However, the actual process of producing distilled water is typically less cost-effective because it takes much longer, and boiling water requires a lot of electrical energy.

Deionized water has a faster production process. A deionization system also needs power, but it takes minutes, rather than hours, to produce a batch of deionized water. The disadvantage of deionizers is their high upfront cost.

So, a water distiller is cheaper upfront but has higher running costs, while a DI water purification system is more expensive but cheaper to run in the long term.

βš–οΈ Deionized Vs Distilled Water: Which Is Better?

So, comparing distilled water vs deionized water, which is best? Ultimately, the best water type for you depends on your situation.

For instance, if you want to treat your drinking water, we think a distiller is the best water purification system because it removes all harmful impurities. Using a DI system to remove dissolved ions from your water won’t protect you from all possible drinking water contaminants.

Many of the other at-home uses of deionized and distilled water can be used with either water source. If, for example, you just want to fill your iron, both distilled and DI water are mineral-free and won’t leave scale deposits, so they’re both suitable for this purpose.

In our opinion, distilled water is best in most situations because it has virtually no dissolved solids whatsoever.

❔ Frequently Asked Questions

Can I use deionized water instead of distilled?

Yes, in the majority of cases, you can use DI water can instead of distilled water. However, keep in mind that deionized water may still be contaminated with impurities like chemicals and bacteria. In some situations, high-purity distilled water is the only water type that should be used For instance, dentistry mouth rinsing, wound cleaning, and medical surgery, all need 100% purified water.

Is deionized water safe to use in my CPAP?

Yes, you can use deionized tap water in your CPAP as a last resort if you don’t have distilled water on hand. DI water lacks minerals, so it won’t cause scale formation in your CPAP machine. However, experts recommend using high-purity distilled water in your CPAP because of its guaranteed lack of all impurities, including chemicals, pathogens, and contaminants that aren’t removed by the deionization process.

How do you make deionized water from distilled water?

You could technically make deionized water from distilled water by running the distilled water through a deionizing machine. However, distilled water is already deionized because it has had all its charged ions removed. So, you may as well save the time and effort.

  • Jennifer Byrd
    Water Treatment Specialist

    For 20+ years, Jennifer has championed clean water. From navigating operations to leading sales, she's tackled diverse industry challenges. Now, at Redbird Water, she crafts personalized solutions for homes, businesses, and factories. A past Chamber President and industry advocate, Jennifer leverages her expertise in cutting-edge filtration and custom design to transform water concerns into crystal-clear solutions.

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