High alkalinity in drinking water is a common issue for many homeowners, often leading to problems that affect both taste and household plumbing. High concentrations of alkaline compounds can give water a metallic, soapy, or baking soda-like taste. Excessive alkalinity can also impact the efficiency and lifespan of household appliances.
Understanding Water Alkalinity Versus pH
Alkalinity and pH are related but measure different aspects of water chemistry. The pH value is a measure of the water’s acidity or basicity, specifically indicating the concentration of hydrogen ions (H+) on a logarithmic scale from 0 to 14. Alkalinity, by contrast, refers to the water’s buffering capacity, which is its ability to neutralize acids and resist changes in pH.
This buffering effect is primarily due to dissolved basic compounds, including bicarbonates (HCO3-), carbonates (CO32-), and hydroxides (OH-). High alkalinity means the water contains a large reserve of these ions, allowing it to absorb significant acid amounts before the pH level drops. While high alkalinity typically results in a high pH, alkalinity measures the capacity to resist change, and pH measures the current acidity or basicity.
Practical Reasons for Reducing Alkalinity
The most common consequence of high alkalinity is the formation of scale, which is a build-up of mineral deposits. This scaling occurs when the concentration of dissolved minerals, especially calcium and magnesium carbonates, exceeds their solubility limits, often accelerated by heating. The mineral deposits reduce the efficiency of heat transfer in appliances like water heaters and boilers, leading to higher energy consumption and premature equipment failure.
High-alkalinity water can also negatively affect specialized water uses, such as hydroponics or aquariums, by causing undesirable pH swings. Although not a health threat at typical levels, high concentrations of alkaline ions impart an objectionable bitter or soapy taste to drinking water. This “salty” or “soda” taste is particularly noticeable when hydroxides or large amounts of bicarbonates are present.
Consumer-Level Reduction Methods
Reverse Osmosis
Reverse Osmosis (RO) is one of the most effective methods for reducing alkalinity by removing the dissolved solids responsible for it. The RO system works by forcing water under pressure through a semi-permeable membrane that rejects a high percentage of ions and molecules. This process strips the water of mineral ions like calcium, magnesium, and bicarbonates, which significantly reduces the water’s total dissolved solids (TDS) and its buffering capacity.
Since RO removes the buffering capacity, the resulting purified water often has a slightly acidic pH, typically falling between 5 and 7. This occurs because the water has lost the minerals that stabilize its pH, making it susceptible to absorbing atmospheric carbon dioxide to form carbonic acid. Many modern RO systems include a final remineralization stage to reintroduce beneficial minerals and restore a neutral pH.
Distillation
Distillation is a purification process that physically separates water from all non-volatile contaminants, including the minerals that cause alkalinity. The process involves boiling the water to create steam and then condensing the steam back into liquid water, leaving behind all dissolved solids. This method is highly effective because the alkaline compounds cannot vaporize with the water, virtually eliminating all total alkalinity.
Similar to RO water, distilled water has almost no buffering capacity, and its pH can drop to an acidic level, sometimes as low as 5.8, due to carbon dioxide absorption from the air. Distillation units are available for home use but are generally slower, use more energy, and produce a flatter-tasting water.
Acid Dosing
Controlled acid dosing is a method that chemically neutralizes the alkaline compounds in the water. Acids react with the bicarbonates and carbonates, converting them into carbonic acid, which reduces the overall alkalinity of the water. For consumer applications, food-grade acids like citric acid or acetic acid (vinegar) are the safest options for small-scale adjustments.
Citric acid is a common choice because it is relatively safe to handle and does not add new mineral nutrients. However, this method requires careful and precise measurement to prevent over-correction. Over-correction could result in highly corrosive water that accelerates the leaching of metals from plumbing. Automated acid injection systems are available for whole-house treatment, but they require significant monitoring and maintenance.
Ion Exchange
Specialized ion exchange systems can also be used for dealkalization, operating on a different principle than standard water softeners. Weak Acid Cation (WAC) resins are designed to remove cations like calcium and magnesium that are associated with alkalinity. As the water passes through the resin beads, the alkaline-forming ions are exchanged for hydrogen ions (H+), which reduces the alkalinity and lowers the pH.
Another option is a chloride cycle anion dealkalizer, which uses a strong base anion resin to exchange the negatively charged bicarbonate and carbonate ions for chloride ions (Cl-). While these systems are highly effective at targeting alkalinity, they are less common for general drinking water applications than RO and are often employed in conjunction with other treatment methods.
Monitoring and Maintaining Water Quality
Testing the water is fundamental both before and after any reduction system is installed to ensure the desired quality is achieved and maintained. Alkalinity is typically measured in parts per million (ppm) or milligrams per liter (mg/L) as calcium carbonate (CaCO3). Consumer-level water test strips or titration kits provide a simple way to measure total alkalinity and pH at home.
For drinking water, the ideal alkalinity range is between 20 and 200 ppm, offering sufficient buffering without causing excessive scale formation. Systems like RO require regular maintenance, including timely replacement of pre-filters and the membrane, to ensure consistent performance. Maintaining a consistent alkalinity level is important because water with low buffering capacity can become corrosive, potentially leaching metals like lead and copper from pipes.