Is Your Drinking Water Acidic? A Comparison of the Varied pH of Popular Bottled Waters

Introduction

Research substantiates that consumption of acidic beverages such as soft drinks and sports drinks is positively correlated with the incidence and prevalence of dental caries and dental erosion.^1-3 Dental erosion has been defined as the chemical removal of mineral from tooth structure.⁴ Erosion of enamel and root surfaces of teeth is a potentially serious oral health concern in the U.S., and the consumption of acidic beverages is a contributing factor.¹ The overall consumption of carbonated soft drinks in the U.S. is continually increasing, with between 56 and 85% of school-age children consuming at least 1 per day.⁵ The pH of most soft drinks is within the range of 2 to 4, indicating that it is very acidic. When the teeth are bathed in the acid from these drinks, they become susceptible to demineralization. Demineralization occurs when acidogenic bacteria, specifically Streptococcus mutans, colonize in the oral cavity, forming dental biofilm.⁶ The biofilm metabolizes carbohydrates (such as sugars commonly found in soft drinks), which acidifies the saliva. The normal pH of the oral cavity is about 6.3, and when the pH falls below 5.5, tooth structure begins to demineralize.⁵ The literature suggests that the lower the pH of the beverage, the higher the rate of demineralization of enamel.¹ Soft drinks are not the only acidic beverages that pose an oral health challenge in the U.S.; many Americans consume coffee and sports beverages as well, which are also acidic. Cochrane et al studied the pH of various sports drinks, finding that while not as low as Coca-Cola®, many Gatorade® and Powerade® drinks also had an acidic pH leading to dental erosion when tested.⁷ While dental erosion can affect any individual, some are at increased risk for demineralization and, subsequently, dental caries. People with xerostomia (due to decreased saliva to buffer the acid content in the mouth), mouth breathers and those with orthodontic brackets are at increased risk for erosion.⁵

Acidosis is a pathologic condition of increased hydrogen ion concentration in blood and body tissues, and occurs when arterial pH falls below 5.55.⁸ Harmful effects of acidosis may include increased bone resorption and decreased osteoblastic function, as evidenced in a study conducted by Brandao-Burch et al who found that as arterial pH drops, mineralization of bone reduces.⁹ Alkaline mineral water (by definition, water with naturally occurring minerals such as calcium and magnesium and a pH above 7) has been shown to be therapeutic in decreasing bone resorption, increasing bone density and improving hydration.^10-12 Naturally alkaline artesian well water is beneficial due to its acid-buffering capacity and has been shown to be effective in adjunctively treating gastric reflux disease.^12,13 Additionally, there is some evidence that an alkaline diet may slow the progression of some chronic diseases, such as hypertension, muscle wasting and strokes.¹⁴

It is important for the oral health care provider to be aware of the relative acidity of the beverages consumed daily and how they affect oral health. Some waters, primarily bottled waters which people generally believe are safer than tap water, are actually acidic and potentially harmful to the teeth. For the reasons listed above, consumption could pose a threat to the oral and overall health of those who consume acidic water. Water's mineral content determines its pH and is dependent upon the source, in addition to the purification process.

Prior to discussing specific brands, it is necessary to distinguish between different types of bottled water. Natural spring water is derived from specific natural springs, where the earth filters it naturally. Some springs are naturally alkaline, while others are more acidic. Natural spring water is typically filtered and disinfected using processes including, but not limited to activated carbon filtration to remove added chlorine, microfiltration to remove particles and ultraviolet light sanitation to destroy bacteria.¹⁵ The original mineral content of the natural spring water is retained during the filtration process, thus making the pH correspond exactly to the alkaline (or acidic) mineral content of the water. Another term for the total mineral content of water is total dissolved solids (TDS), which refers to the inorganic and organic substances present in solution in water and able to survive filtration through a small filter.¹⁵ TDS constituents include, but are not limited to, calcium, sodium, potassium, magnesium, chloride, sulfate and nitrate.¹⁵ Artesian well water comes from a confined aquifer containing groundwater under positive pressure.¹⁶ Like natural spring water, it also retains its mineral content during filtration. The pH of artesian water will depend on the acidity or alkalinity of the artesian well. Purified drinking water is derived from a public water supply of a given area and then filtered by reverse osmosis, distillation or another process.¹⁷ The mineral content in the water is removed during the filtration process, and some brands subsequently add minerals and/or electrolytes for taste. Because the alkaline minerals are removed during filtration, it is possible that purified drinking water will have a lower pH than naturally occurring spring or well water (depending on the nature of the source).

Alkaline water, or mineral water, is becoming increasingly popular worldwide, but it is important to distinguish between naturally occurring alkaline (mineral) water and alkaline ionized water. It is not possible to differentiate between the two based on pH alone. The U.S. Food and Drug Administration requires naturally occurring alkaline water to contain at least 250 parts per million TDS from a geologically and physically protected underground water source, and the water is not to contain added minerals.¹⁸ Naturally occurring alkaline water contains a high concentration of minerals directly from the source, and its pH corresponds exactly to its mineral content. Alkaline ionized water is source-independent (and frequently starts as tap water); the water pH is altered through electrolysis, or the splitting of the water molecule into hydrogen and hydroxide ions with an electric current.¹⁹ Therefore, the alkaline pH is created artificially, and does not match the mineral content of the water. Ionized water can be produced with a home appliance called a water ionizer, or can be purchased commercially. Proponents of alkaline ionized water claim that it is an antioxidant, increases hydration and energy, and can even slow the aging process.¹⁹ However, there is a lack of scientific research available to support these claims. In fact, one clinical trial involving rats detected damage to the myocardial muscle following the consumption of alkaline ionized water.^20-22

A clinical trial by Koufman and Johnston found naturally occurring alkaline water (pH 8.8) to be therapeutic in the treatment of acid reflux disease.¹³ Alkaline water was found to denature human pepsin 3b, which is the enzyme that breaks down protein in the digestion process.¹³ Sufferers of acid reflux experience painful, burning sensations due to acidic foods and beverages activating the pepsin that has been pushed into the airway from the stomach. It is imperative to recognize that this study highlighted the therapeutic benefits of naturally occurring alkaline water, as opposed to alkaline ionized water.

Equipped with a knowledge base on the important differences between types of bottled waters, the dental hygienist will be better prepared to educate and inform patients about water consumption. However, awareness of the water's pH and TDS value (which is often not found even online) will also play an important role in the provider's patient recommendations. The aim of this study was to research, test and compare specific brands and types of bottled water for potential acidity.