The pH of pure water is 7, which is considered neutral on the pH scale. However, the pH of water can vary depending on dissolved substances.
Understanding pH
The pH scale measures how acidic or basic a substance is. It ranges from 0 to 14:
- 0-6: Acidic
- 7: Neutral
- 8-14: Basic (or alkaline)
pH is determined by the concentration of hydrogen ions (H+) in a solution. A high concentration of H+ ions indicates acidity, while a low concentration indicates alkalinity.
pH of Pure Water vs. Real-World Water
- Pure Water: In a perfectly pure sample of water (H2O), the concentrations of hydrogen ions (H+) and hydroxide ions (OH-) are equal. At 25°C (77°F), this balance results in a pH of 7.
- Real-World Water: Water in the real world, such as tap water, river water, or bottled water, almost always contains dissolved minerals, gases, and other substances. These impurities can alter the pH. For example, dissolved carbon dioxide can lower the pH, making the water slightly acidic. As a result, the pH of drinking water typically falls between 6.5 and 8.5.
Factors Affecting Water pH
Several factors can influence the pH of water:
- Dissolved Minerals: Minerals like calcium carbonate can increase pH, making the water more alkaline.
- Dissolved Gases: Gases like carbon dioxide can decrease pH, making the water more acidic.
- Temperature: Temperature can affect the pH of water, although this is usually a small effect.
- Pollution: Industrial or agricultural runoff can introduce acidic or basic substances into water sources, significantly altering their pH.
Importance of Water pH
The pH of water is important for several reasons:
- Aquatic Life: The pH of water significantly impacts aquatic ecosystems. Most aquatic organisms thrive within a narrow pH range.
- Drinking Water Quality: The EPA recommends that drinking water pH be between 6.5 and 8.5 for optimal taste and to minimize the corrosion of pipes.
- Chemical Reactions: pH affects the rates of many chemical reactions, including those important in industrial processes and environmental systems.
In summary, while pure water has a neutral pH of 7, natural and treated water sources typically have a pH between 6.5 and 8.5 due to dissolved substances. This pH range is essential for both environmental and human health.
