The pH scale, which ranges from 0 to 14, is a logarithmic measure of the concentration of hydrogen ions in an aqueous solution. A pH value of 7.0 represents a perfectly neutral substance, like pure water, where the balance between acidic hydrogen ions and basic hydroxide ions is equal. Anything below 7.0 is considered acidic, and anything above 7.0 is considered basic, or alkaline. While pure water sits at a neutral 7.0, tap water is rarely found at this exact midpoint because of dissolved minerals and intentional adjustments made during the treatment process. Public drinking water is instead regulated to fall within a specific and tightly controlled range.
The Definition of Neutrality and Tap Water’s Typical Range
Tap water is almost never perfectly neutral but is instead typically slightly basic, or alkaline. The United States Environmental Protection Agency (EPA) recommends that municipal water systems maintain the pH of drinking water within a range of 6.5 to 8.5. Because the scale is logarithmic, a change of just one whole unit represents a tenfold change in acidity or alkalinity.
Utilities often aim for the higher end of the recommended range, specifically targeting a slightly alkaline pH. This small adjustment is made to protect the vast network of pipes that deliver the water to homes and businesses. Water that is slightly basic tends to be less corrosive, which helps to mitigate the deterioration of water distribution infrastructure.
Key Factors That Determine Local Water pH
The pH level of tap water is shaped by two primary influences: the geology of the source water and the subsequent treatment processes. For instance, water sourced from areas with limestone or dolomite bedrock, which contain calcium carbonate, tends to naturally dissolve these minerals, resulting in harder and more alkaline water with a higher pH.
Conversely, water originating from mountain runoff or boggy areas often has a lower pH, making it naturally softer and more acidic. This is due to the presence of decaying organic matter and the effect of rainwater, which is slightly acidic because of atmospheric carbon dioxide.
Municipal utilities then step in to stabilize the water’s pH before distribution. They intentionally adjust the water’s chemistry by adding buffering agents like lime (calcium hydroxide) or soda ash (sodium carbonate). These compounds increase the water’s alkalinity, helping to counteract any natural acidity and prevent the water’s pH from fluctuating dramatically.
Why pH Levels Matter for Health and Home Infrastructure
The pH level of your tap water is a significant factor in determining the longevity of your home’s plumbing and the overall safety of your drinking water. Low, acidic pH is highly corrosive, acting as a solvent that can dissolve metal components from pipes and fixtures. This corrosion can lead to the leaching of heavy metals, such as copper and, more significantly, lead, into the water supply. Exposure to lead poses a serious health hazard, especially for children and pregnant women.
While acidic water is the main culprit for metal leaching, excessively high, alkaline pH levels also present infrastructure problems in the form of mineral scaling. Alkaline water, often characterized as “hard water,” encourages the precipitation of minerals like calcium and magnesium, which form hard deposits inside pipes and water-using appliances. This scaling can restrict water flow and decrease the efficiency and lifespan of hot water heaters and other appliances.
Regarding direct health effects, regulated tap water within the EPA’s recommended pH range is generally safe to drink. However, water with a pH substantially outside this range can affect aesthetics; acidic water may have a bitter, metallic taste, while highly alkaline water can taste like baking soda or feel slippery.
Testing and Adjusting Water pH at Home
Simple litmus test strips offer a quick, color-coded estimate of pH, while digital pH meters provide a more precise numerical reading. For the most accurate and comprehensive results, especially if metal leaching is suspected, a professional laboratory water analysis is the most reliable option.
If testing reveals a pH level outside the optimal range, consumers can take steps to adjust it. For water that is too acidic, a neutralizing filter, often containing calcite, can be installed to slowly dissolve minerals and raise the pH. Conversely, a reverse osmosis system, while effective for purification, can sometimes lower the pH, making it necessary to follow it with a remineralization cartridge to bring the pH back into the desirable range.