Water is classified as “soft” when it contains a very low concentration of dissolved minerals, specifically calcium and magnesium. These two minerals are responsible for what is commonly known as “hard water.” When a water softener is installed in a home, it actively removes these hardness ions to prevent scale buildup on pipes and appliances. The safety of drinking softened water depends on the specific chemical changes introduced during the treatment process and the health profile of the person drinking it.
Understanding the Softening Process
Residential water softeners operate using a principle called ion exchange. Inside a tank filled with tiny, negatively charged resin beads, the beads are initially saturated with positively charged sodium ions. As hard water flows through the resin, the calcium and magnesium ions are chemically attracted to the resin beads. This stronger attraction causes the hardness minerals to displace the weaker sodium ions. The calcium and magnesium ions become trapped on the resin, and in exchange, an equivalent number of sodium ions are released into the water.
The Primary Concern: Increased Sodium Levels
The most significant chemical consequence of water softening is the introduction of sodium into the drinking water supply. The total amount of sodium added is directly proportional to the initial hardness of the water being treated. For every one grain per gallon (GPG) of hardness removed, approximately eight milligrams (mg) of sodium are added per liter of water. For example, water with a moderate hardness of 10 GPG would have about 80 mg of sodium added per liter. While this amount is generally not a concern for healthy adults, this small increase is relevant for individuals on severely sodium-restricted diets, such as those managing hypertension or certain kidney conditions. Softened water should also not be used to prepare infant formula, as a baby’s underdeveloped kidneys are not equipped to handle the increased sodium load.
The Impact of Missing Hardness Minerals
Softened water lacks the calcium and magnesium that were present in the original hard water. Although these minerals contribute small amounts to daily dietary intake, the vast majority of calcium and magnesium comes from food sources. Therefore, the absence of these minerals in drinking water does not typically pose a nutritional deficiency risk for people with a balanced diet. A more serious health concern arises from the chemical properties of the mineral-depleted water. Soft water is inherently more aggressive and corrosive, which can lead to the leaching of trace metals, such as copper and lead, from older metal plumbing components into the drinking supply.
Practical Drinking Water Solutions for Softened Homes
Several practical solutions exist to ensure safe drinking water. The most straightforward approach is to install a bypass line that directs the main cold water supply away from the softener unit to a designated drinking tap, typically the kitchen sink. This provides unsoftened water for drinking and cooking, while the rest of the home benefits from the softened supply. Another effective solution is installing a point-of-use reverse osmosis (RO) system, which removes up to 90% of dissolved sodium and other impurities. Alternatively, a softener using potassium chloride instead of sodium chloride salt can be used, replacing hardness ions with potassium.