Tap water should not be too acidic or basic. It usually measures around a 7, or neutral, on the pH scale of 0 to 14. Neutral tap water typically has a better flavor and keeps your indoor plumbing running smoothly. If you have an especially acidic or alkaline water supply, a filter or water injector can help balance tap water pH.
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Impact of pH Imbalance
Water with a slightly acidic pH level of less than 6.5 may contain elevated levels of iron, manganese and other toxic metals. It's considered "soft" water and could break down metal piping -- leaching metals from the pipes into your water supply. Acidic water also has an unpleasantly sour or metallic taste and may leave bluish stains on your sinks and laundry. Overly alkaline water, which measures greater than an 8, can taste bitter, like flat club soda, and also corrode piping. It's not unsafe to drink this "hard" tap water, but it can form deposits on dishes and make it hard to lather soap when washing.
Why pH Varies
The pH level of your tap water is largely affected by the source of the drinking water and the type of minerals found locally in rock. Pollution and acid rain can also affect tap water pH. Measure your water's pH using litmus paper -- just drop a bit of water onto it and watch the color change to indicate the pH value. Drinking water is normally between 6 and 8.5 on the pH scale.
Neutralize tap water at its point of entry into your home. A neutralizing filter balances your tap water by moving the water through a system and passing it through a filter containing a neutralizing substance. When the pH is greater than 6, calcium carbonate is used to treat the water and bring it up closer to 7. Synthetic magnesium oxide neutralizes water with a pH lower than 6.
An alternative to a neutralizing filter, which requires maintenance and risks overhardening your water, is soda ash or acid injections. Soda ash, also known as sodium carbonate, raises the pH levels of overly acidic water when added to a water system. Install a home system for injection that neutralizes the tap water at the point of entry. Note that people on low-sodium diets should be wary of using sodium carbonate for neutralization and need to consult a doctor before installing. For overly hard, or alkaline, water, use an acid injection system. Acetic acid, found in vinegar, citric acid or alum, are used to bring the pH value closer to 7. Injection systems need regular maintenance and replacement of the chemicals, which may require special handling.
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.