The question of what alkalinity drinking water should be often confuses consumers seeking a specific pH number for health reasons. Water quality involves a complex interplay of chemistry, infrastructure protection, and aesthetic concerns like taste and odor. The acidity or basicity of water is measured by pH, which relates to the concentration of hydrogen ions. Understanding the scientific distinction between pH and alkalinity is the first step toward interpreting official water quality standards and evaluating consumer health claims.
Defining pH and Alkalinity in Water
Water chemistry differentiates between pH, which measures the intensity of acidity or basicity, and alkalinity, which measures the capacity to neutralize acid. The pH scale runs from 0 to 14, where 7 is neutral, lower numbers indicate acidity, and higher numbers indicate basicity. This measurement is a logarithmic scale representing the concentration of hydrogen ions (\(\text{H}^+\)) present in the water.
Alkalinity describes the water’s buffering capacity, which is its ability to resist changes in pH when an acid is introduced. This capacity is primarily determined by the concentration of dissolved compounds, such as bicarbonate (\(\text{HCO}_3^-\)), carbonate (\(\text{CO}_3^{2-}\)), and hydroxide (\(\text{OH}^-\)) ions. Alkalinity is measured in milligrams per liter (\(\text{mg/L}\)) as calcium carbonate (\(\text{CaCO}_3\)). Water with high alkalinity contains more of these compounds and requires a greater amount of acid to lower its pH, demonstrating a stronger buffering effect.
A common misunderstanding is that a water sample can have a high pH (basic) but low alkalinity, meaning it has a weak buffer and its pH could shift easily. Conversely, water with a neutral pH of 7 could have high alkalinity, making its pH stable despite the introduction of acidic substances. This distinction is important for water treatment and infrastructure management, where pH stability is often more significant than the precise pH value itself.
Standard Regulatory Ranges for Drinking Water
The recommended pH range for municipal drinking water is established primarily for practical reasons related to water distribution systems, not direct human health. The U.S. Environmental Protection Agency (EPA) sets a Secondary Maximum Contaminant Level for pH between 6.5 and 8.5. This secondary standard addresses aesthetic qualities like taste and odor, as well as the functionality of the plumbing.
Water with a pH below 6.5 is acidic and can be corrosive, leading to the leaching of heavy metals like lead and copper from pipes into the drinking supply. This metal contamination presents a health concern, but the low pH itself is the infrastructure issue that enables the leaching. Water with a pH above 8.5 can contribute to scaling, which is the buildup of mineral deposits inside pipes, reducing their efficiency and shortening the lifespan of appliances.
Maintaining the pH within the 6.5 to 8.5 range helps control corrosive and scaling tendencies, ensuring infrastructure longevity. The World Health Organization (WHO) notes that water within this range is acceptable for consumption. Therefore, regulatory bodies recommend this range primarily because it protects plumbing and ensures acceptable taste.
Examining Health Claims of High-pH Water
Many consumers are interested in water outside the standard regulatory range due to the marketing of high-pH or “alkaline water,” which often has a pH between 8.0 and 10. Proponents suggest this water can neutralize body acidity, provide superior hydration, and offer other health benefits. The human body maintains its blood pH within a tight, slightly alkaline range of 7.35 to 7.45 through effective homeostatic mechanisms involving the lungs and kidneys.
The digestive system quickly buffers any ingested water; stomach acid typically has a pH between 1.5 and 3.5, and alkaline water is temporarily neutralized upon entry. While there is no scientific evidence that drinking alkaline water significantly alters the body’s overall pH balance, some studies have explored specific, localized effects. For example, research suggests that water with a pH of 8.8 may help inactivate pepsin, an enzyme responsible for acid reflux, potentially providing relief for some individuals.
Other minor studies have indicated that high-pH water may reduce blood viscosity after strenuous exercise, which proponents claim suggests improved hydration. However, the clinical significance of this finding is not fully established. The scientific consensus is that the body’s regulatory systems render the consumption of high-pH water largely irrelevant to systemic pH balance. For most healthy people, water within the standard regulatory range is entirely safe and sufficient, and the potential benefits of high-pH water remain unsubstantiated.