Water alkalinity measures the capacity water has to neutralize acid. This capacity is closely linked to the pH scale, a logarithmic measure of hydrogen ion concentration in a solution. A pH of 7 is considered neutral, with values below 7 being acidic and values above 7 indicating alkalinity. The water’s final pH level depends on the presence of dissolved alkaline substances.
Defining Extreme Alkalinity and the pH Ceiling
The concept of extreme alkalinity is governed by the theoretical limits of the pH scale for aqueous solutions. The scale ranges from 0, representing the highest acidity, to 14, representing the highest alkalinity in a standard aqueous solution. This number is derived from the negative logarithm of the hydrogen ion concentration.
This inverse relationship means that as the concentration of hydrogen ions decreases by a factor of ten, the pH increases by one whole unit. While a pH of 14 is the theoretical maximum for a highly concentrated basic solution, the highest pH for a consumable water product is significantly lower. Water with a pH above 10 is rarely sold for general daily consumption.
The practical ceiling for alkaline drinking water is considered to be around pH 9.5 to 10. Highly alkaline water can present potential hazards, even if it is not chemically caustic. Water exceeding pH 10 can affect the taste, often making it bitter, and may interfere with normal digestion and mineral absorption upon excessive consumption.
Water with a pH above 11 is not considered safe for internal consumption by humans and is reserved for non-potable applications. Extreme alkalinity can cause problems such as skin and eye irritation, which is why commercial drinking products are managed to stay within the practical and safe consumption range.
Regulatory Standards for Safe Water pH
The highest pH level considered safe for human consumption is defined by regulatory guidelines and practical health considerations. The U.S. Environmental Protection Agency (EPA) sets non-mandatory guidelines for public drinking water through its National Secondary Drinking Water Regulations (NSDWRs). The EPA recommends a maximum pH of 8.5 for public water systems, an aesthetic standard intended to control pipe corrosion and prevent bitter taste.
This pH range of 6.5 to 8.5 is not a health-based standard but guidance for public water systems to maintain palatability and manage infrastructure. The pH of bottled water is regulated by the Food and Drug Administration (FDA), which treats bottled water as a food product. The FDA’s regulations must be at least as stringent as the EPA’s, yet they do not impose a specific maximum pH limit for bottled water.
This regulatory distinction allows commercially available bottled alkaline waters to often exceed the EPA’s 8.5 guideline, with many products falling between pH 9 and 10. While the FDA does not set a maximum, the accepted highest safe limit for long-term daily consumption is around pH 10. Consuming water with a pH significantly higher than this on a regular basis may interfere with the body’s natural acid-base balance, though individual tolerance varies.
Methods Used to Achieve High pH Levels
Water achieves high pH levels through two primary mechanisms: natural mineral content and artificial ionization.
Natural Alkalinity
Naturally alkaline water gains its higher pH from contact with geological formations, such as limestone, which introduces dissolved salts and minerals. The primary compounds responsible for this natural alkalinity are bicarbonate (HCO3-) and carbonate (CO3 2-) ions, along with hydroxides (OH-) of minerals like calcium and magnesium.
This mineral content gives the water a buffering capacity, meaning it can resist changes in its pH when an acid is introduced. The pH of natural alkaline water is generally stable and tends to range from pH 8 to 9.5, depending on the source rock and mineral concentration.
Artificial Ionization
The second method involves artificial ionization, often achieved using a device called a water ionizer. This process uses electrolysis, where water is passed over platinum-coated titanium electrodes separated by a membrane. A direct electrical current is applied, which causes the water to separate into two streams: one acidic and one alkaline.
At the negative electrode (cathode), hydrogen ions (H+) are converted into hydrogen gas (H2), reducing the H+ concentration in that stream. This reduction leads to an increase in the water’s pH, generating the alkaline stream. Artificially ionized water can reach higher short-term pH levels, sometimes up to pH 11 or more, but this alkalinity may be less stable than that derived from natural mineral sources.