Reverse Osmosis (RO) vs Deionized (DI) Water

Wondering whether you can swap RO (reverse osmosis) water for DI (deionized) water, or vice versa, for cleaning, drinking, or other household uses?

In this quick guide, we’ve outlined the key differences between deionized water and reverse osmosis water. By the end, you should know which water type best suits your needs.

📌 Key Takeaways:

  • Deionized water is made by the deionization process, and is free from all ions (electrically charged molecules or atoms) found naturally in a water supply.
  • Reverse osmosis water is made by the reverse osmosis process, which uses a semipermeable membrane in a multi-stage filtration system, and is free from all impurities, including ions.
  • Reverse osmosis water is completely pure and has a very low total dissolved solids count, while deionized water still contains impurities that aren’t electrically charged, such as chemicals and some dissolved metals.

🆚 Deionized Water Vs Reverse Osmosis Water: The Differences

What’s the biggest difference between reverse osmosis and deionized water?

RO water is entirely pure, while DI water is simply free from charged ions.

Below, we’ve shared the key features of reverse osmosis and deionized water, and how these differ in each water type.

Filtration Process

Reverse Osmosis

Reverse osmosis tap water is produced in a reverse osmosis system.

A reverse osmosis filter system has numerous stages of filtration, including a sediment filter, two carbon filters, and a semipermeable membrane. It’s this membrane that produces purified water by rejecting all contaminants larger than its pores (usually 0.0001 microns).

Water is forced at a high pressure through the membrane, and the rejected contaminants rebound into the RO chamber, where they’re flushed away down a drain. The purified water passes through the membrane and into a storage tank, ready for drinking.

Reverse osmosis filters are most commonly installed as point of use units, often underneath a kitchen sink or on a kitchen countertop.

Reverse osmosis water filtration system shows multiple filter stages

Deionization

Deionized water is produced in a water deionizer, sometimes known as an ion exchange system or an ionizer.

A deionized water system doesn’t use physical filters to remove ions. Instead, a DI resin is used to bind and attract charged ions (such as minerals and salts) in water.

There are two types of resins: one with a positive charge and one with a negative charge. The positively charged resin attracts negatively charged ions, and the negatively charged resin attracts positively charged ions.

Some deionizers use several water filters to produce deionized, filtered water, but this isn’t a guarantee.

A water deionizer is typically installed as a POU system and installed in an inline cartridge housing.

mixed bed deionization

Contaminants Removed

Reverse Osmosis Water

A reverse osmosis water filtration system produces purified water that’s free from virtually all dissolved organic chemicals, heavy metals, salts, minerals, microorganisms, and most other organic and inorganic contaminants. An RO system is considered the best water filtration system for people who want to purify water for drinking, cleaning, and other uses around the house.

There are only a few contaminants that might not be fully removed by RO water purification systems, including some chlorine byproducts, organic compounds, and some dissolved gases like carbon dioxide.

Want on-demand purified drinking water? See our reviews of the best value-for-money reverse osmosis systems in 2022 👈

Deionized Water

Deionized water is water that has no charge because all of its ions have been removed. The deionization process removes contaminants like salt, minerals (such as magnesium and calcium), carbon dioxide, and some organic impurities – but not the dissolved solids.

DI water has a very low ion concentration, but it still contains metals, chemicals, microorganisms, and other harmful contaminants found in tap water.

Different types of contaminants in drinking water

Uses

Reverse Osmosis Water

RO water can be used for any application that requires pure water, such as cleaning, filling aquariums, irons, and steamers, and drinking.

Reverse osmosis water is safe to drinksafer than normal tap water, in fact, because the RO purification process removes dangerous impurities – but mineral-free water has a “flat” taste that many people find unpleasant.

Deionized Water

Deionized water can also be used in aquariums, cleaning, humidifiers, and car AC systems, as well as any other application that requires mineral-free water.

Drinking deionized water is considered safe, but isn’t advised as a long-term habit. Because DI water is free from all mineral contaminants, it’s more susceptible to metal leaching, and it may absorb ions in your body, decreasing your mineral supply.

🔎 What’s Better: RO Or DI Water?

There is no “better” water type. Whether RO or DI water is best for you depends on what you plan to use the water for.

👨‍⚖️ If you need the purest form of water possible that’s free from microbiological contaminants, reverse osmosis water is best. But if you just need water that’s free from electrically charged impurities, or you want to use soft water, DI water is best.

For drinking, both types of water are suitable, but reverse osmosis is safest since it’s guaranteed to be free from pathogens.

❔ Deionized Water Vs Reverse Osmosis Water: FAQs

Is RO better than DI?

Yes, RO is better than DI for people looking to achieve the purest water possible. But deionized water might be better suited to your needs if you just want soft water or water that’s free from all ions.

Is RO and DI water the same?

No, RO and DI water aren’t the same. RO water is produced by membrane separation, while DI water is produced by deionization. Reverse osmosis removes all impurities from water, while deionization removes all ions from water by attracting these impurities to electrically charged resins.

Can you drink RO DI water?

Yes, you can drink RO and DI water. However, because both water types don’t contain trace minerals and salts, they’re known for tasting quite flat.

Is distilled water same as deionized water?

No, distilled water and deionized water are two separate water types. Distilled water is made by boiling water until it evaporates, then sending the water vapor into a separate chamber to condense, while deionized water is made by exposing water to an electrically charged resin, which attracts minerals and salts. Distilled tap water is much purer than deionized water.

Does a water softener produce deionized water?

No. A water softener simply exchanges ions with other ions (using the ion exchange process) – it doesn’t remove all ions entirely. Only a deionizer system can do this.