The widespread belief that all bottled water is pure and perfectly neutral has been challenged by growing evidence of its variable pH levels. Contrary to popular assumption, many common bottled waters have an acidic pH, which can have implications for your health and nutrition. Understanding the factors that contribute to this acidity is key to making informed hydration choices.
The Role of Carbon Dioxide
One of the most common reasons for bottled water to be acidic is the presence of carbon dioxide ($CO_2$). This occurs in two main ways:
- Natural Absorption: Even in still (non-carbonated) water, $CO_2$ from the atmosphere can dissolve into the water. This creates a weak carbonic acid ($H_2CO_3$), which lowers the pH from a neutral 7 to a slightly acidic level, often around 5. The chemical reaction is: $CO_2(aq) + H_2O(l) \rightleftharpoons H_2CO_3(aq) \rightleftharpoons H^+(aq) + HCO_3^-(aq)$. The presence of these hydrogen ions ($H^+$) is what increases acidity.
- Intentional Carbonation: For sparkling or carbonated bottled waters, $CO_2$ gas is intentionally dissolved into the water under pressure to create the signature fizz. This process rapidly forms carbonic acid, which can give these drinks a pH as low as 3 or 4, making them significantly more acidic than still water.
Impacts of Purification and Processing
Many bottled water brands undergo intense purification processes that can alter their natural pH balance. These methods, designed to remove impurities, can inadvertently strip the water of important, naturally occurring minerals that act as buffers against acidity.
- Reverse Osmosis (RO) and Distillation: Processes like RO and distillation produce very pure, mineral-free water. While this removes contaminants, it also leaves the water with a low mineral content, making it highly susceptible to absorbing atmospheric $CO_2$ and becoming acidic. Without the buffering capacity of minerals like calcium and magnesium, the pH can drop quickly.
- Added Minerals: To improve taste, some companies add a mineral blend to purified water, but these additions do not always fully compensate for the lost minerals. The final pH of these products can still be on the acidic side.
Plastic Packaging and Leaching
Another contributing factor to the acidity of bottled water is the packaging itself. Plastic bottles, particularly when exposed to sunlight or stored for long periods, can leach chemicals into the water.
- Aged and Sun-Exposed Plastic: Studies have shown that the abiotic degradation of aged plastic releases dissolved organic carbon compounds, which can lower the water's pH. This effect is amplified by exposure to sunlight and prolonged storage.
- Chemical Release: The leaching process can release organic acids and other compounds from the plastic polymers, directly contributing to increased acidity. This effect has been observed even in laboratory settings, with significant drops in pH from water stored with aged plastic.
Health Implications of Acidic Water
While occasional consumption of mildly acidic water is generally not a concern, long-term or excessive drinking of highly acidic water could have health impacts.
- Dental Erosion: The most commonly cited concern is damage to tooth enamel. When the pH in your mouth drops below 5.5, tooth enamel begins to demineralize, weakening the teeth and increasing the risk of cavities and sensitivity. Highly acidic bottled waters, especially flavored or sparkling types, pose a significant risk.
- Digestive Issues: For some individuals, particularly those with acid reflux or sensitive stomachs, consistently drinking acidic water may exacerbate symptoms like heartburn and stomach pain.
- Potential for Metal Leaching: Highly acidic water is corrosive and can leach heavy metals like copper and lead from plumbing systems, which could be a risk for consumers of acidic tap water. However, this is less of a concern with bottled water unless it's an unusually acidic brand or contaminated during production.
A Comparison of Water pH
To put the acidity of bottled water in context, here is a comparison with other common water sources:
| Factor | Sparkling Bottled Water | Purified Bottled Water | Natural Spring Water | Municipal Tap Water |
|---|---|---|---|---|
| Cause of Acidity | Carbonic Acid (intentionally added $CO_2$) | Susceptible to atmospheric $CO_2$ absorption due to mineral removal during purification (RO/distillation) | Can be naturally slightly acidic depending on the source rock, but often balanced | Often pH-regulated by municipalities to maintain a neutral or slightly alkaline range of 6.5-8.5 |
| Potential pH Range | 3.0–6.0, often very low | 5.5–7.5, can be acidic | 6.5–8.5, generally balanced | 6.5–8.5, regulated |
| Dental Health Impact | High risk for enamel erosion due to strong acidity | Potential for erosion, especially for brands with lower pH levels | Lower risk for enamel erosion due to balanced pH; some have beneficial minerals | Low risk, and often contains fluoride which strengthens enamel |
| Leaching from Plastic | Yes, can occur especially with aging bottles and sun exposure | Yes, similar to other bottled types | Yes, depends on packaging material and age | Not a factor when consumed directly from the tap or a non-plastic container |
Making Informed Choices
If you are concerned about the acidity of your drinking water, here are some practical steps you can take:
- Read Labels: Look for water labels that specify the pH level. Many brands of naturally alkaline water, such as Essentia or Icelandic Glacial, advertise a pH of 8 or higher.
- Choose Spring Water: Natural spring water often has a more balanced pH due to its mineral content. Look for brands that bottle at the source and specify the pH.
- Test Your Water: You can purchase a simple pH testing kit, like indicator strips or a digital meter, to test the water yourself. This is an easy way to check the acidity of both your tap and bottled water.
- Filter Tap Water: High-quality home water filters or ionizers can help balance the pH of your tap water while removing impurities.
- Consider Alkaline Drops: For a convenient option, you can add alkaline drops to your water to increase its pH.
Conclusion
While the convenience of bottled water is undeniable, not all products are created equal in terms of pH. The reasons behind the acidity are diverse, ranging from the natural absorption of $CO_2$ and the effects of rigorous purification to the leaching of chemicals from plastic packaging. Awareness of these factors is crucial for anyone focusing on a balanced nutrition diet, especially concerning dental health. By making informed choices, such as opting for naturally alkaline water or using tap water filters, you can ensure your daily hydration supports, rather than compromises, your overall well-being.
Visit the U.S. Environmental Protection Agency to learn more about drinking water standards.
