What is Reverse Osmosis Water?

Learn more about our team of experts & our testing process here.

What makes reverse osmosis water special? We've all heard the phrase since our high school chemistry, but yet most people are confused abotu what it actually is.

Quick Jump -

If you are a reader of health ezines or offline health publications, there’s no doubt you’ve encountered the popular buzz phrase, “reverse osmosis water.” If you are still crinkling your forehead and asking yourself, “What is reverse osmosis water” you are certainly not alone. There is much confusion on this topic and the purpose of this article is to clear up this confusion.

What is Osmosis?

Before you can understand reverse osmosis, you first need to understand osmosis. Osmosis is a natural process that occurs in the human body, throughout all living organisms, and throughout all ecosystems.

It is the scientific principle whereby a weaker salt solution will always have the tendency to migrate across a semi-permeable membrane into a stronger salt solution. This occurs passively without adding energy or forcing anything to happen. The same would occur with any solvent, such as sugar, dissolved in an aqueous solution (water solution).

Try this simple experiment!

There’s a simple and fun experiment you can perform with your kids that will drive home what osmosis is and give you a visual of the process…

Fill your bathtub with water. Next, fill one balloon with ordinary tap water out of the same faucet. Fill another balloon with salt water. You can just use ordinary table salt.

The amount of salt doesn’t matter much but you can use a ratio of three parts water to one part salt to make your salt water. Before the water balloon fight breaks out, drop both of these balloons into the bath water and watch what happens over time.

The balloon containing tap water should stay about the same size because the bath water and the water inside the ballon have about the same concentration of solvents (no added salt). The balloon filled with salt water should start to expand because the weaker solution, the bath water, should start to move inside the ballon with the stronger solution, salt water.

How about those swollen feet?

Here’s another example you can think about. When you soak your tired swollen feet in water containing a high concentration of Epsom salts, what happens? The swelling goes down! This is because of the magic of osmosis!
The weaker solution, the water in your swollen feet, moves toward the stronger solution, the Epsom salt water! Like magic, the swelling in your feet goes down!
Let’s look at another example. When you notice that your favorite houseplant looks wilted and unhappy, what do you do? You water it of course! What happens? It perks up, right? This is due to the magic of osmosis! The fresh water you add to your plant naturally gravitates inside the plant where the solution of minerals is much stronger.
Please note that a stronger solution will never gravitate toward a weaker solution during osmosis.
This is a universal truth in nature. Keep this in mind as we explore reverse osmosis.

What is Reverse Osmosis?

Here’s another example you can think about. When you soak your tired swollen feet in water containing a high concentration of Epsom salts, what happens? The swelling goes down! This is because of the magic of osmosis!

Unlike osmosis, which is a natural process, reverse osmosis is NOT a natural process. In order to get this reverse osmosis to occur, considerable energy must be applied from an outside force. Basically, considerable pressure is applied to force a stronger solution past a semi-permeable membrane into a weaker solution.

Reverse osmosis may happen inside a water purification machine or during an industrial process. Extreme pressure, i.e. extreme FORCE, is applied to a stronger solution to forcibly move it past a semi-permeable membrane. In this process, the substances dissolved or suspended in the water are removed.

Another way to say this is that reverse osmosis is the exact opposite process (reverse process) from osmosis. However, it is not natural for reverse osmosis to happen and it must be artificially induced by an outside force. Generally speaking, the force required to perform reverse osmosis must be generated by a machine as force applied by a human would not be strong enough.

What is Reverse Osmosis Water?

Many people automatically equate reverse osmosis water with alkaline water. However, you should not make this assumption. Strictly speaking, reverse osmosis water is actually acidic water, i.e. it has a pH of less than 7.0.

This is because water that has been run through a reverse osmosis process has had most of the particulates suspended in the water removed. This includes mineral ions and bicarbonate that buffers water and keeps it alkaline. Without minerals and bicarbonate, water is acidic, not alkaline.

Reverse osmosis is often used to “purify” water. It’s quite an effective way to remove harmful substances like pathogenic bacteria, pyrogens (harmful fever producing substances released by pathogenic bacteria), chlorine, lead, and other heavy metals. However, there’s also a negative side to using reverse osmosis to purify water. It filters out the good stuff too!

This includes healthy minerals like calcium, magnesium, potassium, selenium, and silica. Reverse osmosis also filters out bicarbonate which has also been shown to have positive effects on the human body and even increase the bioavailability of minerals.

The reason that people often think that reverse osmosis water is alkaline water, or a type of alkaline water, is because many brands of bottled alkaline water use reverse osmosis as part of their process (so do many consumer end water machines). However, it is only a FIRST STEP when they do so.

After running the water through reverse osmosis, they then take additional steps that makes the water alkaline again. This may include running the water after reverse osmosis through another filter that adds minerals back into the water. It may also include adding in bicarbonate.

Some companies or water machines that make “alkaline water” first use reverse osmosis and then use electrolysis (ionization) to “ionize” it, i.e. run it past electrodes that create ions from the water molecules.

In Summary

Strictly speaking, reverse osmosis water is acidic, not alkaline. This is because reverse osmosis removes the minerals and other substances required for water to maintain an alkaline state.

However, in the vernacular, people sometimes mistakenly use the term “reverse osmosis water” to mean alkaline water that has used this process as the FIRST STEP in treating the water. This is why you should never accept these terms at face value. Always check to see how the water has been treated, every step used.