Alkalinity and pH are distinct measurements of water chemistry. The pH scale measures the concentration of free hydrogen ions, determining if a substance is acidic (below 7), neutral (7), or alkaline (above 7). Alkalinity, by contrast, measures a liquid’s capacity to neutralize acids, known as its buffering capacity. This capacity comes from dissolved ions like bicarbonates, carbonates, and hydroxides that absorb acid protons. This process stabilizes the pH and prevents large fluctuations, but high alkalinity itself can create systemic problems for human biology or the environment.
Impacts on Human Physiology
When highly alkaline water (typically pH 9 or higher) is consumed, the immediate interaction occurs in the stomach. The stomach maintains an acidic environment (pH 1.5 to 3.5) using hydrochloric acid to break down food and eliminate pathogens. Introducing high-pH water can temporarily neutralize or dilute this acid, potentially compromising the stomach’s natural protective barrier and digestive function.
This temporary reduction in acidity can interfere with pepsin, an enzyme necessary for efficient protein breakdown. This disruption may lead to mild gastrointestinal discomfort or, rarely, skin irritation in sensitive individuals. The body’s internal pH is tightly regulated by homeostatic mechanisms, maintaining blood pH in a narrow range of 7.35 to 7.45. The kidneys and lungs constantly manage this balance, meaning the pH of consumed water has little effect on the body’s overall systemic pH.
Long-term consumption concerns center on the potential for metabolic alkalosis, though this is rare from typical drinking water. Excessive alkalinity can interfere with the absorption of certain minerals, such as calcium. It also poses a risk for individuals with pre-existing kidney conditions. For example, consuming water with a pH above 9.8 can be risky for people with kidney disease due to the potential for hyperkalemia (high potassium levels).
Alkalinity’s Effects on Ecosystems
High alkalinity acts as an ecological stressor, particularly in natural aquatic and terrestrial environments. Most aquatic life, including fish and invertebrates, is adapted to a pH range between 6.5 and 9.0. When the pH rises above 9.0, organisms experience physiological stress that impairs their ability to regulate salt and water intake, potentially damaging gills and skin.
A dangerous consequence of high pH is the alteration of chemical toxicity, specifically ammonia. As pH increases, the relatively harmless ionized ammonium converts to toxic, un-ionized ammonia, which is far more damaging to aquatic life. This means a moderate increase in alkalinity can turn a manageable pollutant level into a lethal hazard for fish populations. The buffering capacity of high alkalinity also prolongs the ecological imbalance by making it difficult for natural processes to correct the pH.
For soil and plant life, high alkalinity is detrimental because it directly impacts nutrient availability in the root zone. When irrigation water with high alkalinity is repeatedly applied, the dissolved carbonates and bicarbonates increase the soil’s overall pH. This increase causes essential micronutrients, such as iron, manganese, and zinc, to become insoluble and chemically “locked up.” The resulting iron deficiency is a common issue, manifesting as chlorosis (yellowing of the newest leaves while the veins remain green).
Systemic Consequences of High pH
Beyond biological systems, high alkalinity causes significant physical problems in managed water infrastructure, primarily through mineral deposition. This process, known as scaling, occurs when water with high concentrations of dissolved minerals (calcium and magnesium carbonates) is heated or undergoes a pH shift. High alkalinity maintains the necessary buffering capacity and high pH, which promotes the precipitation of these minerals out of the solution.
Scaling leads to a hard buildup on surfaces, reducing the efficiency and lifespan of appliances. This is noticeable in water heaters, boilers, and heat exchangers, where mineral deposits act as an insulator, requiring more energy. In plumbing systems, the narrowed diameter of the pipes reduces water flow and increases pumping costs. High alkalinity also complicates the maintenance of recreational water systems, such as swimming pools, where high levels make it difficult to adjust the pH, leading to cloudy water and scale formation.
Testing and Correcting High Alkalinity
Managing high alkalinity begins with accurate testing to determine the water’s buffering capacity. Simple home tests, such as colorimetric test strips or liquid reagent test kits, provide a quick estimate of total alkalinity, often measured in parts per million (ppm). For precise measurements necessary for engineering solutions, a water sample should be sent to a professional laboratory for detailed titration analysis.
Correcting high alkalinity involves adding an acid to neutralize the excess bases and reduce the buffering capacity. In large-scale systems, this is achieved through automated acid injection using mineral acids like sulfuric or hydrochloric acid. Homeowners dealing with high alkalinity in pools or spas use liquid hydrochloric acid (muriatic acid) or granular sodium bisulfate (dry acid). Gardeners can address high soil pH by incorporating acidic organic amendments like peat moss or by using acid-forming fertilizers.