Distilled vs Deionized Water: The 2021 Definitive Comparison

Distilled vs Deionized Water

There’s no denying that having so many water treatment options nowadays is a great thing. But it can also be pretty confusing, especially if you’re relatively new to the market and you’re still in the process of researching your options.

Two popular water treatment options, aside from filtration, are distillation and deionization. They might sound like terms you left behind in your high school science classes, but fear not: they’re just fancy words to describe two relatively similar methods of treating water.

In this guide, I’ll be helping you to get to grips with distilled and deionized water, including their differences, uses, and costs.

Is There a Difference Between Distilled Water and Deionized Water?

You’ll come across a select few things in life, such as car batteries, humidifiers and essential oil diffusers, that advise against using standard water from your tap. Instead, manufacturers suggest that either distilled or deionized water can be used, as this water has had certain harmful impurities removed.

Don’t be so quick to think that distilled and deionized water are the same, though, as both have a few differences that are worth knowing about.

What is Distilled Water?

Distilled water is demineralized water that is completely pure – meaning that it contains no metals, chemicals, or other impurities.

To produce distilled water, tap must be boiled and condensed into a clean carafe. Distillation is one of the most effective water purification processes to currently exist.

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Water distiller

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 water treatment machines known as deionizers, which allow you to manually adjust water’s pH.

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DI system

Uses of Deionized Water vs Distilled Water

Both distilled and deionized water are considered “pure”, which means they’re often used interchangeably in applications that require a pure water source. Bear in mind that distilled water is the purest of the two, as the process of evaporating and condensing water removes even the smallest contaminants, while deionized water may theoretically still contain pathogens like bacteria.

Deionization water is usually used in cooling applications, industrial processes, and manufacturing. At home, this type of water is used in your fish tank and your car’s battery.

On a large scale, distilled water is commonly used to sterilize medical equipment, in the production of beauty products, and in laboratory applications. This type of water can be used for a number of household purposes including topping up your steam iron or car cooling system, watering your plants, or filling aquariums.

deionized water used in laboratory

Deionized Water vs Distilled: Contaminants Removed

Both deionized water and distilled water are very pure. However, they undergo a different treatment process to produce a slightly different end result.

The distillation process removes the largest amount of particulates. Minerals, salts, chemicals, pathogens, metals, and pretty much everything aside 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. Usually, a distiller will come with a post-filter, typically made from activated carbon, which can remove any lingering contaminants from water as it condenses into a container.

Deionized water has had its ions – i.e. the inorganic charged particles – removed. To produce the purest deionized water, it should be filtered beforehand to remove any organic substances. You’d get the best result by using reverse osmosis alongside deionization. Reverse osmosis filters water so thoroughly that only a trace amount of ionized minerals will need to be removed by deionization.

Related: Distilled vs Reverse Osmosis water: Key Differences

Difference in Cost Between Distilled vs Deionized Water

If you’re considering distillation vs deionization for personal uses at home, you should be aware of the cost difference of producing each water source.

Water distillation takes the longest and requires a power source, which, while not expensive, is still a cost to be aware of. The more water you’re trying to distill, the longer it’ll take, which is why distilling water is often less cost-effective in factory applications. In some cases, such as in medical situations, water may need to pass through a distiller twice or even three times, increasing costs significantly.

Deionized water, on the other hand, has a faster production process. The quickest way to make deionized water is to use a deionizer – a machine that contains a mixed ion exchange resin bed that’ll alter water’s pH as it passes through. Again, this system will need power, but because it takes minutes, rather than hours, to produce a batch of deionized water, a deionizing unit would use far less electricity than water distillers.

While both have their pros and cons, cost-wise, distilled water is slightly more expensive to make than deionized water. Of course, if you’re just looking to create a batch of high purity water at home, you’re probably working from less of a “time is money” approach, so if you don’t mind the distillation process taking longer, there’s not a massive difference between the two.

Frequently Asked Questions

Can I Use Deionized Water Instead of Distilled?

In the majority of cases, DI water can be used instead of distilled water – but bear in mind that deionized water may still be contaminated with impurities like bacteria.

There are several situations in which you should never replace distilled water with deionized water, as only the highest purity water should be used. Dentistry mouth rinsing, wound cleaning, and medical surgery, for instance, need purified water that’s 100% free of the bad stuff.

Can I Use Deionized Water in My CPAP?

No. Experts recommend only using high-purity distilled water in your CPAP machine, so DI water won’t cut it in this case. You don’t want to risk breathing in certain pathogens and contaminants from deionized tap water. Some contaminants may also wear down the materials that make up your CPAP, which could completely break the system after a while.

Is Distilled Water of Deionized Water Better For Drinking?

Both types of water are more likely to be used in a laboratory setting, but you can distill your tap water for drinking, if you want. The benefit of drinking distilled water is that it doesn’t contain any of the bad stuff; however, some people think it tastes a bit flat because of its lack of mineral content.

Deionized water, on the other hand, shouldn’t be used as drinking water, as it’s corrosive. Drinking water that’s deionized could damage your tooth enamel and even your soft tissues, so it’s best to keep it out of your body. Plus, there’s no guarantee that deionized drinking water isn’t contaminated with bacteria and other harmful pathogens, which may not be removed entirely in your pre-filter process.

How Can I Store My Purified Water?

Distilled water tends to last for longer than deionized water, but if you plan to make distilled drinking water, you will probably notice that it tastes stale after several days. To prolong the shelf life of drinking water that’s been distilled, store it in an airtight glass container (avoid plastic or metal containers that could leach contaminants into the water).

High purity deionized water typically doesn’t last as long, as it quickly reacts with carbon dioxide in the air. However, if you’re not producing a batch of deionized purified water to have it used immediately, you could also store it in an airtight glass container.

DI Water Vs Distilled Water: Which Is Best?

It depends on what you’re looking for from each source. Water that’s been distilled is more suitable for drinking, but many at-home chores are flexible enough to allow you to interchangeably use each source. Water that has undergone a distilling process, however, is the best in my eyes, as it has virtually no impurities whatsoever.