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Home » Water Education & Testing » What Is the pH of Reverse Osmosis Water?- Why Is RO Water Acidic?

What Is the pH of Reverse Osmosis Water?- Why Is RO Water Acidic?

By: Stephanie Nielsen
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Water quality is paramount to our overall health and well-being, and one of the key aspects of this quality is its pH level. The pH of water can impact everything from its taste to how it interacts with pipes and appliances and even its effects on the human body. 

Reverse osmosis is a popular method of water filtration that provides many benefits, but it also affects the pH of the water. So, if you’re wondering, “what is the pH of reverse osmosis water?” You’ve come to the right place.

In this article, we’ll explore the pH of reverse osmosis water, explaining why it tends to be slightly acidic and offering ways to adjust its pH. We’ll also compare it to the pH of other types of water and provide information on testing your water’s pH at home.

Let’s get started.

Understanding the pH of Water

The term pH stands for ‘potential of Hydrogen’ and is used to measure the acidity or alkalinity of a substance. The pH scale ranges from 0 to 14. A pH of 7 is neutral, signifying an equal amount of hydrogen and hydroxide ions. A pH below 7 indicates an acidic substance, which has a high concentration of hydrogen ions, whereas a pH above 7 is indicative of an alkaline or basic substance with more hydroxide ions.

Ph scale of water in a circular chart

What Exactly Is Acidity?

Acidity is a fundamental concept in chemistry and is used to describe the concentration of hydrogen ions (H+) in a solution. High levels of concentration of hydrogen ions result in a lower pH value, making the water acidic. 

Acidic water can have a sour taste and can corrode metals, causing certain types of plastic to deteriorate. It can also leach metal ions from the plumbing system, leading to metallic-tasting water and staining laundry and appliances. These metal ions include: 

  • Iron
  • Manganese
  • Copper
  • Lead
  • Zinc

While the acidic nature of a solution, including water, is a significant aspect of its chemical nature and potential interactions, it’s critical to maintain a balanced acidity level to avoid undesired effects such as sour taste, corrosion, and potential metal contamination.

What Exactly Is Alkalinity?

Alkalinity, in contrast, refers to the capacity of water to resist changes in pH that would make the water more acidic. In other words, alkalinity is a measure of the ability of a solution to neutralize acid to the equivalence point of carbonate or bicarbonate. The greater the alkaline content, the greater the ability of water to neutralize acids. 

Alkaline water, with a pH above 7, often tastes bitter and is believed to neutralize acid in the human body.

Impact of pH Level on Water

Water pH, as a crucial determinant of water quality, plays a pivotal role not only in the taste and smell of the water but also in the broader health context, influencing several factors directly linked to our well-being.


Firstly, pH significantly affects the water’s taste. Water that is highly alkaline or highly acidic tends to have an unpleasant taste. Acidic water can taste sour or metallic, while alkaline water can taste bitter or soda-like. Drinking water with a neutral pH generally provides a much cleaner, more refreshing taste.


The smell of the water can also be influenced by its pH. For instance, overly acidic water could lead to the corrosion of pipes, causing a metallic smell. On the other hand, excessively alkaline water might promote bacterial growth, which can produce a variety of odors.


In a more direct link to health, the pH of water can influence the water’s ability to harbor life. This factor is crucial in natural bodies of water, as it can directly affect the ecosystem and the health of aquatic life. A balanced pH level supports biodiversity, while extremes in pH can be harmful or even lethal to many organisms.

Moreover, the pH of water plays a crucial role in the solubility of minerals and nutrients. Many minerals, including those beneficial to our health, are sensitive to pH. 

For example, minerals like calcium and magnesium, which are essential for bone health, have reduced solubility in water with low pH levels. Drinking water that’s been treated to have a balanced pH can, therefore, be a good source of these essential minerals.


Lastly, pH affects the effectiveness of many disinfectants. Chlorine, for instance, is a common disinfectant used in water treatment, and its ability to kill bacteria and other harmful microorganisms changes with pH. 

As pH increases, the disinfecting power of chlorine decreases. Therefore, maintaining a balanced pH in water is crucial for ensuring its safety and suitability for consumption.

Understanding these facets underscores the importance of regularly testing and, if necessary, adjusting the pH of the water we consume. Whether it’s reverse osmosis water or tap water, achieving a balanced pH can have both direct and indirect benefits for our health and wellness.

The pH of Reverse Osmosis Water

Reverse osmosis water, popularly known as RO water, has a pH that falls typically in the range of 5 to 7, making it slightly acidic. However, this pH can vary based on the composition of the feed water and the specific reverse osmosis system used.

Why Is Reverse Osmosis Water Acidic?

Reverse osmosis is a water purification process that removes impurities by using pressure to force water molecules through a semipermeable membrane. During this process, water is forced against the membrane, causing contaminants to be filtered out and flushed away.


One of the key reasons RO water is acidic lies in the purification process itself. The RO membrane is selective and removes larger molecules and ions, such as calcium and magnesium, from the water. These ions, which contribute to the hardness and alkalinity of water, are thus significantly reduced. This leaves the water with a higher concentration of hydrogen ions relative to hydroxide ions, resulting in a lower pH or increased acidity.

Carbon Dioxide

Another reason for the acidity is the carbon dioxide (CO2) factor. The RO membrane allows water molecules and smaller ions, including CO2, to pass through. When CO2 dissolves in water, it forms carbonic acid, which further decreases the pH of the water. Therefore, the more CO2 present in the feed water, the lower the pH of the RO water.

How to Improve the pH of Reverse Osmosis Water

While RO water is safe to drink, some people may be concerned about the slightly acidic nature of the water. Various methods can be employed to increase the pH of RO water, effectively reducing its acidity.

Remineralization Filters

Remineralization filters work by adding essential minerals back into the water post the RO process, thus increasing the pH. The water filter typically contains calcium, which dissolves in the water, raising the pH and giving the water a more natural taste.

iSpring RO500AK-BN Tankless RO Water Filter System

Alkaline/Ionizer Machines

Alkaline water machines, also known as water ionizers, work by electrically separating the incoming water into two streams. One stream is more alkaline, and the other is more acidic. You can use the alkaline water for drinking and the acidic water for cleaning.

Lime Softening

A water softener option frequently use is lime. Lime softening is an industrial process that involves adding lime (calcium hydroxide) to the water. The lime reacts with the water’s acidity to form calcium carbonate, a neutral substance, reducing the overall acidity of the water.

Learn More: RO VS. Water Softener: Which Is Best For Your Home?

Soda Ash or Sodium Bicarbonate

Adding soda ash or sodium bicarbonate to the water can also neutralize its acidity. These compounds react with the hydrogen ions in the water, reducing their concentration and thus increasing the pH.

pH Neutralizers

pH neutralizers are systems that inject a solution of soda ash or sodium hydroxide into the water. The solution mixes with the water, neutralizing the acid and raising the pH.

In my personal experience, the simplest way to get my RO system to produce the levels I prefer for my drinking water is with remineralization filters.

RO Water pH Compared to Other Water Types

Comparing the RO water pH to other types of water gives us a broader perspective on the subject and helps us understand where each water stands in terms of acidity and alkalinity.

Water TypeTypical pH Range
Reverse Osmosis (RO)5-7
Tap Water6.5-8.5
Bottled Water6.5-7.5
Distilled Water7
Alkaline Water8-9

As you can see, compared to sink water, bottled water, and alkaline water, reverse osmosis water tends to be more acidic. However, it’s important to remember that slightly acidic water isn’t necessarily harmful to consume. 

Regardless, for those who prefer more alkaline water, there are options to adjust the pH of reverse osmosis water, as mentioned above.

How to Test pH of a Reverse Osmosis System At Home

Understanding the pH level of your water is crucial as it can affect various aspects such as taste, plumbing systems, appliances, and even your health. While professional laboratory testing can provide a comprehensive and accurate profile of your water’s pH and other chemical components, it may not be the most practical or cost-effective solution for everyone, especially if regular testing is desired. 

Also Check Out: Best Water Test Kits + Guide

Thankfully, testing the pH of water coming from home is a simple and accessible process that can be accomplished using several great methods. These methods range from quick and easy-to-use products like pH test strips and drops to more sophisticated yet highly accurate tools like digital pH meters. 

Here are a few different ways you can test the pH of your water right in the comfort of your own home.

pH Test Strips

pH test strips are easy-to-use tools that provide a quick estimation of pH. You immerse the test strip in the water, and it changes color based on the pH. You then match the color of the strip with a color chart that comes with the test kit to get the pH value.

Digital pH Meter

A digital pH meter provides a more accurate measurement of pH. It has an electrode that you immerse in the water, and it provides a digital readout of the pH.

pH Indicator Solutions

Also known as pH drops, these solutions change color when added to the water. The color corresponds to a certain pH range. They are less accurate than digital meters but are relatively cheap and easy to use.

Laboratory pH Testing

For the most accurate results, you can also send a sample of your water to a laboratory for professional pH testing. This service often includes testing for other water quality parameters.

Final Thoughts

RO water is slightly acidic due to the nature of the reverse osmosis process. However, it is important to note that drinking slightly acidic water will not cause harm to the human body. Our bodies have excellent pH buffering systems. 

So long as the pH of the drinking water is within the safe range of 6.5-8.5, as outlined by regulatory agencies like the United States Environmental Protection Agency (EPA), it is considered safe to consume and free of contaminants.

Nevertheless, if you are concerned about the slightly acidic nature of your water, you can always opt for methods to increase its pH level. At the end of the day, drinking pure, clean water should be everyone’s goal, and reverse osmosis is a fantastic tool to achieve this.


Is reverse osmosis healthy?

Yes, reverse osmosis is a highly effective method of purifying water. It is considered contaminant free, removing up to 99% of contaminants, including bacteria, viruses, heavy metals, pesticides, and more. However, it also removes some beneficial minerals, so it’s recommended to use a remineralization filtration system in conjunction with a reverse osmosis water system.

Does reverse osmosis water remove healthy minerals from the water?

Yes, the RO process removes many minerals from the water, including beneficial ones like calcium and magnesium. If you are concerned about your water, consider adding a remineralization filter to your RO system, which will reintroduce these beneficial minerals.

Is reverse osmosis acidic or alkaline?

Reverse osmosis water is typically slightly acidic due to the nature of the purification process. However, the pH level can be adjusted by adding minerals back into the water post-filtration or using other pH adjustment methods.

What is the reverse osmosis process?

The reverse osmosis process is a water purification technique that uses a semipermeable membrane to filter out contaminants and unwanted molecules from water. This process works by applying pressure to force water through the membrane, leaving behind the impurities, resulting in clean, purified water.

What is the difference between reverse osmosis and deionization?

RO is a water purification method that effectively enhances the quality of water, achieving purity levels between 90% and 99%. Osmosis deionization (DI) filters, on the other hand, work by swapping positive hydrogen and negative hydroxyl molecules with the positive and negative contaminant molecules present in the water.

Photo of author
Stephanie Nielsen
Stephanie worked as a department supervisor of kitchen, bath, and appliances at Home Depot, and water filters were part of the inventory she was responsible for assisting clients with so she learned the ins and outs of matching the right filtration device to homeowner’s needs. She also worked closely with Culligan water to educate customers about whole-home water treatment and softener systems.

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