The pH of water is a measure of its acidity, and the Environmental Protection Agency (EPA) maintains strict standards for appropriate pH levels in drinking water. A number of factors can affect water pH, and while no municipal drinking water in the United States violates EPA standards for safety, pH provides information about the source and treatment of that water.
According to the University of Rhode Island, pH is "one of the most common analyses in soil and water testing, [and] is the standard measure of how acidic or alkaline a solution is." It notes that pure water is considered neutral, with a pH of 7, and that solutions of pH less than 7 are acidic, while alkaline solutions have pH values greater than 7. According to the university, water pH is generally measured electronically, but may also be analyzed using acid-sensitive dyes on testing strips called litmus paper.
Consuming excessively acidic or alkaline water is harmful, warns the EPA. Drinking water must have a pH value of 6.5-8.5 to fall within EPA standards, and they further note that even within the acceptable pH range, slightly high- or low-pH water can be unappealing for several reasons. High-pH water has a slippery feel, tastes a bit like baking soda, and may leave deposits on fixtures, according to the EPA website. Low-pH water, on the other hand, may have a bitter or metallic taste, and may contribute to fixture corrosion.
Sources of Alkalinity
High pH water can result from dissolved minerals, notes the University of Rhode Island. Groundwater in areas with limestone bedrock, for instance, is commonly higher-pH than glaciated or rainwater. Wastewater contamination of drinking water can also raise pH, due to the presence of chemical detergents and other cleaning agents. Finally, many municipal processing plants artificially increase the pH of water to prevent acid corrosion of pipes.
Sources of Acidity
Water from areas affected by acid rain may have low pH, according to the University of Rhode Island. They also indicate that glacier water is generally lower in pH than groundwater. In particular, dissolved carbon dioxide increases water acidity, which may be significant in drinking water sources but is generally treated during municipal water processing. Wilkes University notes that soda ash, an alkaline chemical, is sometimes used to treat low-pH water, but adds sodium.
Wilkes University points out a further problem associated with drinking water and pH: High-pH water is often hard. They note that hard water "does not pose a health risk, but can cause aesthetic problems." Among problems associated with hard water, they list formation of scale on fixtures, a bitter flavor, difficulty getting soaps to lather, and decreased water-heater efficiency. They suggest that water can be softened with ion-exchange water-softening devices.