What Is The Difference Between Reverse Osmosis Water And Distilled Water

What Is The Difference Between Reverse Osmosis Water And Distilled Water?

There has been a lot of confusion to understand what is the difference between reverse osmosis water and distilled water. In this article, I will fill all the blanks and explain everything.

In essence, the biggest difference between distilled and RO is in the way water is produced. Reverse osmosis water is physically filtered, while distilled is generated by evaporation and condensation methods. Both types are very efficient at removing contaminants although not perfect and still leave specific contaminants.

Let’s learn more about each type of water, how it is generated, and what are the differences.

Reverse Osmosis Explained

Before we can compare RO and distilled water, I think it would be beneficial to understand how both are produced.

Let me explain the reverse osmosis process first which would then make much more sense to you.

The reverse osmosis is one of the most advanced treatment methods currently available. The RO membrane has pores of the size 0.0001 microns. Such size rejects anything more significant than that and in essence, only allows molecules of water and anything smaller than that to pass.

Because pores in a membrane are so small, water has to be forced to pass through the membrane, so you need to generate pressure. Although lots of units work with the standard pressure from the plumbing, some filters have the pump to increase it.

The difference between reverse and regular osmosis is that water moves naturally to the side with a higher number of contaminants or solutes. This is happening when no pressure is applied. The standard osmosis is how plants are absorbing water, as water in leaves has more solutes than water on the leaf. However, once you add pressure, you reverse this process, thus reverse osmosis.

As a result of that, RO is achieving exceptionally high removal rates, usually around 96-99%. It is important also to mention that RO, removes not only contaminants but also minerals that affect the flavor.

The bottom line is that reverse osmosis water is generated using membrane with micropores and pressure.

Distillation Explaineddistillation explained

I hope everything is clear with reverse osmosis. Let’s dive into the distillation and how it generates water.

In essence, the distillation process is simple. Just boil tap water in a container or pot to the point when it starts to evaporate. Step number two would be to have another container that collects evaporated water.

Now, here is the most critical part. You need to create condensation. This is achieved with the help of hot and cold barrier. The barrier basically converts water vapor back to water state as it cools it down. The most obvious way to create a barrier is to use ice.

Almost forgot to remind you to be careful with distilled water. Even though, the cold barrier cools the water down it’s still hot, just in case beware of that when handling.

So, I have explained how does distillation work, let’s talk about what is happening during the process itself.

Boiling is an incredible way to kill bacteria, so as you boil water, viruses, and bacteria such as giardia, cholera, but also E. coli, salmonella and hepatitis are killed.

During the evaporation process contaminants such as hardness minerals, dissolved solid – iron and manganese, or fluoride are left inactive at the bottom of the container. Also, heavy metals and lots of organic compounds remain in the original container. Water that is condensed in a second container is free from the contaminants listed above.

What Is The Difference

I am sure that by now you can confidently tell the difference between both treatment methods and how they work.

We can confidently say that there is no single system that would be perfect, and both RO and distillation are no exception. Let’s discuss what contaminants reverse osmosis and distillation doesn’t remove and compare the results.

What RO Doesn’t Remove

Now, the RO membrane has such small pores that it’s capable of removing an impressive amount of contaminants. However, there is still a certain number of contaminants that are smaller than the pore size, which makes them capable of passing through the membrane. So, let’s have a look at what reverse osmosis is not able to remove.

In general, water molecules are considered to be one of the smallest molecules, but some of the following could be even smaller.

  • Pesticides
  • Herbicides
  • Chlorine
  • Gasses

Pesticides and herbicides are often used in agriculture, to kill pests and insects, but also unwanted weed. Some of these are used to boost growth, which allows growing the crop multiple times per year.

The bottom line is that pesticides and herbicides can be toxic to humans. If you live in a very agricultural rich area, chances are that your water contains some of these. Even though in developed countries, there are certain regulations in place, do not underestimate the protection.

Chlorine is used to disinfect water in pools, but there is also a certain number of treatment plants that are using chlorine and chloramine to process water. Now, what is essential to know is that reverse osmosis does remove chlorine to some extent, but it is not capable of removing all of it.

This is the reason why RO filters usually have other stages with carbon filtration. Carbon blocks are an efficient solution to remove chlorine and pesticides. They work perfectly in pair and what is left by the RO membrane, is removed by carbon block and vice versa.

What Distillation Doesn’t Remove

Distillation also removes a decent number of contaminants, but as well as RO is not perfect.

Similarly to the RO, the biggest problem that distillers have is to remove chemical compounds. The reason why contaminants are left in the water is, these have a boiling point below or close to water. So, they are vaporized with water and collected in the new container.

Here is the list of contaminants, that couldn’t be entirely removed by distillation:

  • Pesticides
  • VOCs
  • Benzene and Toluene

As you can see, there are quite specific contaminants on the list such as benzene and toluene. These are pretty much industrial contaminants, and the probability of having these in standard tap water is low. Regardless of this, however, you must have full information about distillation. Click here to read more about this.

Note that some modern water distillers have a carbon filter installed in them that gets rid of VOCs.

Which Is Better?

I think this section is quite subjective, but I will argue it as objectively as possible.

In my opinion, RO filtered water is better than distilled water.


Well, as I said before both methods leave similar contaminants. However, reverse osmosis filters often come with other stages usually having carbon block cartridges, so it’s not the membrane alone. These ensure to remove remaining contaminants from water.

On the other hand, the distillation process is often misunderstood, and people think that it completely removes all contaminants and doesn’t require any additional treatment. Although, in combination with the carbon block, it would treat water even further.

Both methods also generate a lot of waste. In the RO case, a lot of water is wasted to generate clean water. In the second case, you are wasting electricity or gas to boil and vapor water. From the financial aspect, however, RO comes better out of this because water is cheaper compared to electricity.

Can You Use RO Water Instead of Distilled?

Now, this is quite an interesting question. Let me explain.

You have probably got the idea that RO and distilled water are pretty much similar and differences are negligible. However, I would not recommend substituting distilled water with reverse osmosis water in batteries, for example.

The reason for this is that RO treatment lowers the pH of water and makes it slightly acidic. If you use RO water to replace the liquid in a battery, over time you risk that it will corrode from the inside.

However, distilled water has a neutral pH of 7, which won’t cause corrosion.

The bottom line is that you can use RO water instead of distilled, but I would only use it if there is no other alternative. I would change it back as soon as possible. But don’t be afraid, short term exposure won’t damage the battery as what I am talking about is related to the long term impact.


As you can see, differences between distilled water and RO water are minimal, but despite that, in some cases, you cannot substitute one with the other.

I hope you have a clear understanding now and can comfortably tell the difference.

  • What was the most surprising fact you have learned from this article?
  • Do you prefer RO water or distilled? Why?

Leave your answers in the comment section below.

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8 thoughts on “What Is The Difference Between Reverse Osmosis Water And Distilled Water?”

  1. Looking at difference for use in coffee pots and medical machines such as C-Pap etc., In this time of Corona Virus panic older folks cannot get distilled water. RO could be the solution.

    1. Hi Fred,

      Yes this could be a way potentially, however remember that RO water is slightly acidic. So before using it you will either have to increase it pH or check whether the machine can take acidic water. These are usually very sensitive machines, so I would be careful.

      In terms of using it for coffee pots. Coffee itself is considered to be acidic drink, in fact you can learn more about using RO water for making coffee in my other article on this blog.

      Thanks for stopping by,

  2. That’s my dilemma right now. I’m a senior and can’t find distilled water anywhere for my C-Pap machine. I was going to use RO water in the meantime, but now I’m not sure. I don’t know what is worse, dry breathing or using RO.

    1. Hi Helga,

      Since the previous comment, I have done some research myself gathering information from both manufacturers and users. The outcome is that RO water is a great alternative to use in the meantime for your machine. Certainly much better than tap water full of sediments and minerals that can create deposits inside.

      Thanks for leaving a comment and hope it helps.


      1. Oh that’s wonderful to hear. I was already checking on buying a distilled water maker. Now that I don’t have to that’s just fine with me! Thanks for your quick response. I love your website! It is very informative and easy to read and understand! Keep up the great work. Also, I am looking to get a pump for my RO as it has a 4:1 ratio of wasted water! I had no idea until I read up on your site. You were very helpful and I appreciate your efforts.
        Thanks again,

  3. Yes, I read your article. That’s what gave me the idea to check out the pumps on Amazon. I’m debating on getting the electric pump however I am on a fixed income so if the other pump works well then I may just get that one instead. However if in the long run I can save more money and water with the electric pump I may just invest in that instead. Again, thanks for your feedback. It’s nice to get educated feedback without having to pay for someone’s advice and experience.

    1. Absolutely Helga.

      With permeate pumps though, you wont get as much pressure boost as you would with electric but there will be noticeable difference in terms of wastewater.

      Let me know once you decide, I think it will be interesting for others as well. 🙂


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