The safety of drinking water is often assessed by its pH level, which measures how acidic or alkaline a liquid is. The pH scale runs from 0 to 14, with 7.0 being neutral, values below 7.0 acidic, and values above 7.0 alkaline. Water with a pH of 6.0 is slightly acidic. The central question for consumers is whether this slight acidity poses a direct health risk or an indirect risk through the water delivery system.
Understanding the pH Scale and Regulatory Standards
Pure water naturally holds a neutral pH of 7.0, but water sources in the real world contain dissolved minerals and gases that shift this measurement. For example, rainwater is often slightly acidic because it absorbs carbon dioxide from the atmosphere. Water with a pH of 6.0 is considered to be at the border of what regulators deem acceptable for municipal delivery systems.
Major health organizations recommend that public drinking water systems maintain a pH range between 6.5 and 8.5, classified as a Secondary Maximum Contaminant Level (SMCL). This range is established primarily for aesthetic and structural reasons, such as controlling corrosion and ensuring the water tastes and smells pleasant. While pH 6.0 falls just outside this optimal range, it is not always classified as unsafe to drink, and some regulatory bodies use 6.0 pH as a minimum standard for groundwater systems.
Water with a pH below 6.5 is described as acidic, soft, and potentially corrosive. The slightly acidic nature of pH 6.0 water can sometimes lead to a metallic or sour taste, which is considered an aesthetic issue but is generally not harmful. Concerns about water at this lower pH boundary focus less on the direct effect of acidity and more on how it interacts with plumbing.
Direct Physiological Impact of Slightly Acidic Water
The human body possesses an efficient system for maintaining a stable internal pH, regardless of the acidity of the water consumed. The stomach is naturally very acidic, with a pH ranging from 1.5 to 3.5, which is necessary for digestion. When pH 6.0 water enters the stomach, its slight acidity is instantly overwhelmed by the existing gastric acid.
The body’s acid-base balance is primarily regulated by the bicarbonate buffer system, a complex physiological mechanism involving the lungs and kidneys. This system uses bicarbonate ions to neutralize any excess acid that enters the bloodstream, maintaining the blood’s pH within a very narrow range of 7.35 to 7.45. The volume of acid introduced by drinking a glass of pH 6.0 water is negligible compared to the body’s massive buffering capacity.
The regulation of internal pH ensures that metabolic functions and enzyme activities remain stable. Drinking water with a pH of 6.0 does not pose a threat of causing systemic acidosis or internal harm in a healthy individual. The minimal change in acidity is swiftly managed by the body’s natural processes, making the direct consumption of slightly acidic water a non-issue for immediate health.
Corrosion Risk and Contamination from Water Infrastructure
The more significant public health concern related to slightly acidic water, such as at a pH of 6.0, is its corrosive nature on plumbing infrastructure. Water with a low pH is considered “aggressive” because it tends to dissolve metals from the pipes, solder, and fixtures it contacts. This corrosion is the process by which the slightly acidic water strips away materials like copper, lead, iron, and zinc.
The danger is not the pH of the water itself, but the heavy metal contaminants it carries into the glass after traveling through the pipes. Water below a pH of 6.5 is known to accelerate this leaching process, especially in older homes with lead service lines or copper plumbing joined with lead-based solder. If the water has been sitting stagnant in the pipes for several hours, such as overnight, the concentration of these dissolved metals can be particularly high.
Chronic exposure to these heavy metals, even at low levels, poses serious long-term health risks. Lead is a potent neurotoxin that can cause developmental issues in children and kidney damage in adults. Copper can cause gastrointestinal distress, and long-term exposure to high levels may lead to liver or kidney damage. The corrosivity of pH 6.0 water facilitates the leaching of these toxic substances.
To mitigate this risk in a household with slightly acidic water, a simple action is to run the cold water tap for at least one minute before using it for drinking or cooking. This flushes out the water that has been sitting in the immediate household plumbing, drawing in fresher water from the main supply. Ultimately, homeowners with continuously low pH water may need to consider a neutralizer system to protect both their plumbing and their health from metal contamination.