What Is the pH of Reverse Osmosis Water? Find Out Here!

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One of the biggest concerns people have with consuming reverse osmosis water, is that it may be acidic. After all, drinking acid doesn’t sound like much fun at all, nor does it sound particularly healthy.

But what is the pH level of RO water? Is it really acidic? And if so, is it going to harm your health?

Let’s put it into perspective.

Key Takeaways

  • The pH level of reverse osmosis water is initially around 6.5 but can drop as low as 5 the longer it is exposed to air. This makes RO water slightly acidic.

What Is the pH of Reverse Osmosis Water?

Reverse osmosis water usually has a pH between 5 and 7, but most often sitting at 6.5 before exposure to air and 5 to 5.5 after exposure to air. This is still within the safe drinking range and may only be an issue if you are prone to gastric reflux and need to avoid any acidic beverages.

pH Levels of Other Beverages

While hearing the word ‘acidic’ concerning something you are drinking sounds scary, to put it into perspective, here are the pH values of other common drinks that you probably ingest on a daily basis.

  • Orange juice has a pH of around 3.
  • Black coffee has a pH of 5.
  • Fruit juice can be a 2-4.5.
  • Soft drinks are around 2.5
  • Sports drinks are approximately 3.

All of a sudden, RO water doesn’t look that acidic, does it?

glass of orange juice

Why Is Reverse Osmosis Water Acidic?

During the process of reverse osmosis, minerals are removed from the water, which affects its pH. These minerals are known as alkaline minerals, and the removal process should bring the pH of the water to ‘neutral’, which is a 7 on the pH scale.

However, when water has a pH of 7 and is pure, it loses its buffering capacity. This means it’ll readily dissolve anything it can, and its pH will fluctuate. In the case of RO water, the first thing it is exposed to is air, where it dissolves carbon dioxide. This then creates carbonic acid, which, you guessed it, is acidic. Thus, RO water becomes acidic after purification pretty quickly.

The good news is that the water is still ready to absorb other things and take on the pH of those things too, which can mean it can fluctuate again pretty quickly and can be remineralized with ease – think remineralization filter or mineral blends.

Understanding Water pH and Alkalinity

The scale on which acidity is measured is called the pH (potential hydrogen) scale. 7 is neutral, under 7 is acidic, and over 7 is considered ‘alkaline‘ or a ‘base’. Alkaline water, however, is not to be confused with ‘alkalinity’.

Alkalinity means that water can absorb hydrogen ions without changing its pH, as the minerals in said water will buffer it. As such, some waters with high mineral content can absorb a lot of acid and keep the pH stable.

Lack of Minerals

As reverse osmosis water does not contain minerals that help to buffer the acidic compounds it is exposed to when it interacts with carbon dioxide, the longer you leave the water exposed to air, the more acidic it will become (to about a 5 or 5.5). This is the main reason why reverse osmosis water is acidic.

Lack of Total Dissolved Solids

The lack of TDS in reverse osmosis water leaves it hungry to absorb whatever it can as quickly as it can once it has been filtered. This can cause the pH to fluctuate wildly depending on what it is exposed to. If it were exposed to magnesium and calcium salts before carbon dioxide, then the water wouldn’t become acidic.

How to Test the pH level of RO Water

A fun experiment is to test the pH of your reverse osmosis water upon exit from the system, then after it has been sitting for a while, and then again once it has been remineralized. You can measure the pH in a few ways.

Digital pH Meter

A digital water pH meter is probably the most accurate way to read your water pH. These meters are available online.

  1. Put the pH meter into the container of water.
  2. Press and hold the button.
  3. Wait for the screen to hold a stable reading.

pH Strips

pH strips will indicate the pH of a solution by changing color. You can purchase pH strips at drugstores, and it is best to get ones that fall in the 5-8.5 range. Simply add the strip to the solution and wait for the color change to show.

pH scale

Litmus Paper

Similar to a pH strip is litmus paper, though it isn’t as accurate. It measures acidity and basic but doesn’t get specific about how acidic or how basic a solution is. Considering RO water is a weak acid, it may not even appear acidic on the paper.

The “Red Cabbage” Test

Red cabbage is a fun thing to test water pH with. It has a pigment that changes color based on the pH level of the solution you mix it with.

  1. First, blend up the cabbage with water, and strain the liquid to remove the cabbage chunks.
  2. Secondly, pour the reverse osmosis water into the cabbage liquid, and stir. If it turns red, it is acidic.

Remineralization: How to Make RO Water Alkaline

If you want to ensure your RO water is not even remotely acidic when you drink it, you will need to remineralize it. This can be done in several ways.

Remineralization Filter Stages

Adding a remineralization filtration step is the easiest and most effective way to remineralize your RO water. These can be added to under sink, countertop, and whole house reverse osmosis systems.

They act as final-stage filters and reintroduce calcium, magnesium, and other healthy minerals back into your RO water before you use it.

Mineral Drops, Mineral-Rich Salts, Electrolyte Blends

Mineral drops are an easy way to remineralize your water before drinking. Simply add a few drops into your glass of water before consumption.

Mineral-rich salt is also a cost-effective solution and uses mineral-dense sea salt to add nutrients back into your water. Do not try this with any old salt, as it may not contain all the minerals needed. Himalayan sea salt is often used. Only a quarter of a teaspoon is required to remineralize an entire gallon of RO water.

Electrolyte blends or green blends are other options. These blends contain well-balanced minerals and electrolytes but can be expensive.

Will Drinking Acidic RO Water Harm Your Health?

There is no scientifically validated evidence that reverse osmosis water harms your health. If you have issues with reflux or gastritis, and part of your treatment involves avoiding acidic beverages, then RO water may not be for you unless it has been remineralized.

But generally speaking, the slight acidity of RO water will not harm you, as your body has internal mechanisms to control pH.

If you have any questions about the pH of RO water please don’t hesitate to leave a comment below!

About the Author Gene Fitzgerald

Gene Fitzgerald is one of the founders of BOS and currently head of content creation. She has 8+ years of experience as a water treatment specialist under her belt making her our senior scientist. Outside of BOS, Gene loves reading books on philosophy & social issues, making music, and hiking.
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