Understanding the pH Scale
The pH scale is a measure of a substance's acidity or alkalinity, ranging from 0 to 14. A pH of 7 is neutral, with lower numbers indicating increasing acidity and higher numbers indicating increasing alkalinity. The scale is logarithmic, meaning a substance with a pH of 6 is ten times more acidic than one with a pH of 7, and a pH of 5 is 100 times more acidic. Pure, distilled water starts out with a neutral pH of 7. However, when reverse osmosis (RO) systems process water, the final pH can shift significantly.
Why RO Water is Not Alkaline
The fundamental reason why RO water is not alkaline lies in how the reverse osmosis process works. An RO system forces water through a semi-permeable membrane at high pressure to remove contaminants, including heavy metals, bacteria, and dissolved minerals like calcium and magnesium. While this is excellent for purification, it also strips out the very minerals that act as natural buffers to stabilize water's pH.
The Role of Minerals as Buffers
In unfiltered tap water, naturally occurring minerals like calcium and magnesium bicarbonate help maintain a stable pH level, often making tap water slightly alkaline. When these buffers are removed by an RO membrane, the water's chemistry becomes much more susceptible to change.
Carbon Dioxide Absorption
Because the purified RO water is so pure and lacks mineral buffers, it has an increased capacity to absorb carbon dioxide (CO2) from the air. This absorption creates carbonic acid, which lowers the water's pH and makes it more acidic. In fact, an open glass of RO water can drop from a neutral pH of 7 to around 5.5 within an hour of air exposure.
Is Slightly Acidic RO Water Safe to Drink?
Despite being slightly acidic, RO water is widely considered safe for consumption, and this slight acidity is not a health concern for most people. Many common beverages consumed daily are far more acidic than RO water:
- Coffee (pH ~5)
- Orange Juice (pH ~3)
- Soda (pH ~2.5)
The U.S. Environmental Protection Agency (EPA) recommends a pH range of 6.5 to 8.5 for public drinking water, a guideline primarily established to minimize pipe corrosion, not for health purposes. The human body has sophisticated mechanisms to regulate its own pH levels, and a slightly acidic glass of water will not throw off the body's natural balance.
How to Make RO Water Alkaline
If you prefer to consume alkaline water, there are several simple methods to remineralize your RO water and increase its pH:
Remineralization Options
- Add an alkaline remineralization filter: Many RO systems offer an optional post-filtration stage that adds beneficial minerals like calcium and magnesium back into the water, raising its pH and improving taste.
- Use mineral drops: Concentrated mineral liquid blends can be added directly to your water to increase mineral content and alkalinity with just a few drops.
- Use natural additives: A pinch of Himalayan pink salt or a small amount of baking soda can be used to naturally boost alkalinity, though the precise amount needs careful control.
Comparison of Water Types
| Feature | Reverse Osmosis (RO) Water | Tap Water (Unfiltered) | Alkaline Water (Remineralized RO) |
|---|---|---|---|
| Typical pH | 5.0–7.0 (often 6.0–6.5 in air) | Varies by location, often 6–8 | 8.0–9.5+ |
| Mineral Content | Low (minerals are removed) | Variable (depends on source) | Reintroduced (enriched with minerals) |
| Taste | Flat or neutral | Varied (affected by mineral content and additives) | Fresher, smoother |
| Contaminants | Highly reduced (up to 99%) | Varies (depends on municipal source) | Highly reduced, plus added minerals |
The Health Debate: Separating Fact from Fiction
Some advocates claim significant health benefits from drinking alkaline water, including improved metabolism and neutralizing body acidity. However, the Mayo Clinic notes that there is currently insufficient scientific evidence to support these claims, and a healthy, balanced diet is a more reliable source of minerals. Furthermore, the myth that demineralized RO water leaches minerals from your body is false; your body gets most of its minerals from food.
Conclusion
In summary, RO water is not alkaline; it is typically slightly acidic due to the removal of mineral buffers during the purification process. While safe to drink, its taste can be bland. For those who prefer alkaline water, adding a remineralization filter, mineral drops, or other additives to an RO system can easily raise the pH. The choice between standard RO water and remineralized alkaline water ultimately comes down to personal taste preference and dietary habits, not safety. The key advantage of RO remains its unparalleled ability to provide clean, contaminant-free drinking water.
For more information on drinking water safety standards, you can refer to the U.S. Environmental Protection Agency's (EPA) website.
