Reverse osmosis (RO) systems are trusted for providing safe, clean drinking water free from contaminants. Yet, one of the most common myths surrounding RO water is that it may cause acidity in the body. Some claim that because RO water is slightly acidic in pH, it can disturb digestion, reduce bone health, or trigger acid reflux. But is that really true?
In reality, RO water does not cause acidity in the body. It only measures slightly acidic (around pH 6–6.5) because it lacks minerals that naturally balance pH. The human body tightly regulates its internal pH through the lungs and kidneys, meaning that the acidity of the water you drink has almost no effect on your blood or stomach pH.
This article will clarify the science behind RO water and acidity, explain why this myth persists, and provide practical ways to balance your drinking water for optimal health.
Key Takeaways
- RO water doesn’t cause acidity; its low pH is harmless once ingested.
- The body maintains a constant pH of around 7.4, regardless of water pH.
- RO water’s mild acidity comes from CO₂ absorption and loss of minerals.
- Adding an alkaline or remineralization filter restores balance and taste.
- Proper hydration with RO water actually helps prevent acid buildup.
Understanding Acidity and pH
The pH scale measures how acidic or alkaline a substance is, ranging from 0 (acidic) to 14 (alkaline), with 7 being neutral. For comparison:
| Substance | Typical pH | Classification |
|---|---|---|
| Lemon Juice | 2.0 | Strongly acidic |
| Tap Water | 7.0–7.8 | Neutral to slightly alkaline |
| RO Water (Unmineralized) | 5.5–6.5 | Slightly acidic |
| Alkaline RO Water | 7.5–8.5 | Slightly alkaline |
| Blood (Human) | 7.35–7.45 | Tightly regulated by the body |
As shown above, unmineralized RO water may appear mildly acidic on paper, but this acidity is weak — similar to natural rainwater. The body neutralizes it instantly upon drinking.
Why RO Water Appears Acidic
RO membranes remove nearly all dissolved solids, including calcium, magnesium, and bicarbonates — the minerals that normally buffer pH. When water is stripped of these minerals, it becomes more reactive with carbon dioxide (CO₂) from the air. As CO₂ dissolves, it forms carbonic acid, which slightly lowers the pH.
This does not mean the water is harmful; it simply lacks the natural mineral buffering found in spring or tap water. For reference, distilled water and rainwater have similar pH ranges but are perfectly safe to drink.
To understand how this purification process works, see 14 components of an RO water purifier system.
Does Slightly Acidic Water Affect the Body?
No. The stomach’s natural environment is already highly acidic — around pH 1.5 to 3.5 — to aid digestion. When you drink slightly acidic RO water, it mixes with stomach acid and food, where the pH difference becomes insignificant.
Moreover, your body’s acid-base balance is maintained by complex physiological mechanisms. The lungs control CO₂ exhalation, and the kidneys filter excess acids, keeping blood pH between 7.35 and 7.45. Therefore, the claim that RO water disturbs body pH or causes acidity has no physiological basis.
According to the National Institutes of Health (NIH), drinking low-mineral water has no measurable impact on systemic acidity as long as the diet provides essential nutrients (NIH.gov).
Why the Myth Exists
The misconception stems from two main factors:
- Misinterpreting the pH reading — People assume any number below 7 means the water “causes acidity,” which is false.
- Confusing taste with effect — Slightly acidic water tastes flat or metallic, which some interpret as “acidic” or unhealthy.
The World Health Organization clarifies that slightly acidic water (pH above 5.5) is safe for consumption and has no link to acid-related health issues.
Benefits of Drinking RO Water for Acid Control
Ironically, purified RO water can actually help prevent acidity-related discomfort when compared to contaminated or chlorinated tap water.
Here’s why:
- Removes irritants: Eliminates chlorine and heavy metals that can irritate the digestive lining.
- Supports kidney health: Clean water helps flush acids and toxins.
- Improves hydration: Well-hydrated tissues regulate acid production more effectively.
For example, people suffering from acid reflux often benefit from increased water intake rather than avoiding RO water.
To explore how RO filtration eliminates harmful elements, see does reverse osmosis remove heavy metals.
The Role of Minerals in pH Balance
Calcium, magnesium, and potassium in water act as natural alkalizers. When RO systems remove these minerals, the resulting water has a slightly lower pH. This is why many modern RO units come with a remineralization filter that adds these beneficial minerals back.
Re-mineralized RO water typically achieves a balanced pH of 7.5–8.5 and a TDS of 80–150 ppm, which is ideal for daily drinking. You can read more in best alkaline filter for RO.
Comparing pH Levels in Different Water Types
| Water Type | pH Range | Effect on the Body |
|---|---|---|
| RO Water (Unmineralized) | 5.5–6.5 | Safe; pH neutralized by stomach acid |
| Alkaline RO Water | 7.5–8.5 | May reduce acid reflux symptoms |
| Tap Water | 7.0–7.8 | Neutral, depends on source |
| Bottled Mineral Water | 7.0–8.0 | Naturally buffered with minerals |
| Distilled Water | 5.5–6.0 | Slightly acidic but harmless |
As seen above, the difference in pH between slightly acidic and neutral water is minimal and physiologically insignificant.
Who Should Choose Alkaline RO Water
While standard RO water is safe, alkaline RO water may be more comfortable for people with:
- Chronic acid reflux or GERD symptoms
- Sensitive digestion or gastritis
- Diets high in processed or acidic foods
Alkaline water can temporarily neutralize acid in the esophagus, providing relief from heartburn. However, this is not a treatment — it’s a supportive measure.
For broader insight, see is RO water really safe for daily drinking.
Expert Opinions
Dr. Andrew Nolan, a gastroenterology specialist, explains: “Drinking slightly acidic RO water does not cause acidity or acid reflux. In fact, dehydration and poor diet are much stronger contributors to acid-related issues.”
The WHO also confirms that the acidity of water is not linked to gastric acid production or pH fluctuations in the body. The key is maintaining adequate hydration and mineral intake through diet.
How to Balance RO Water for Better pH
- Use a remineralization or alkaline cartridge — restores natural minerals.
- Store water in glass or stainless steel, not plastic.
- Test your pH regularly with a simple home kit.
- Add natural alkalizers like lemon, cucumber, or Himalayan salt occasionally.
- Keep TDS between 80–150 ppm for healthy balance.
For guidance on pH adjustment, see how to adjust pH of RO water.
Key Points Recap
- RO water’s acidity is mild and does not affect body pH.
- The human body self-regulates acidity, unaffected by water type.
- Re-mineralized RO water has a balanced pH and better taste.
- Hydration plays a stronger role in acid prevention than water pH.
- Myths about RO acidity persist due to misunderstanding of pH values.
FAQs
1. Is RO water acidic in nature?
Yes, slightly. RO water typically has a pH between 5.5 and 6.5, but this mild acidity is harmless and quickly neutralized by your stomach acid.
2. Can RO water trigger acid reflux?
No. There’s no scientific evidence linking RO water to acid reflux or GERD. In fact, proper hydration helps reduce acid reflux symptoms.
3. Should I drink alkaline water instead of RO water?
Both are safe. Alkaline water may feel smoother and can provide short-term relief for acid reflux, but it isn’t medically necessary for everyone.
4. Why does RO water taste flat or sour?
Because it lacks minerals like calcium and magnesium, which give natural water a pleasant taste. A post-filter can restore balance and improve flavor.
5. What is the best pH for drinking water?
The ideal range is 7.0–8.5. Anything between slightly acidic and slightly alkaline is safe and healthy for daily drinking.
Conclusion
Reverse osmosis water does not cause acidity — that’s a myth. Its slightly lower pH is simply a result of CO₂ absorption and mineral removal, not a factor that influences your body’s acid-base balance. The human body regulates internal pH automatically, regardless of the water you drink.
To ensure balanced hydration, use a remineralization or alkaline filter and maintain your RO system regularly. When properly balanced, RO water not only supports digestion but also contributes to overall well-being. For related reading, explore is RO water really safe for daily drinking and best alkaline filter for RO.
Hasan Al Sarker is a Reverse Osmosis Specialist. He has worked for many years to ensure safe drinking water for all. His research paper has been published in several journals, including Issue, Medium, and Slideshare. He is recognized as a water doctor among specialists though he did not attend medical college.
Besides working as a researcher of reverse osmosis technology, he is also very fancy with the kitchen and cooking. His guides are reading thousands of people every day. As a head of content, he is responsible for all the published articles at RO System Reviews.