The question of whether soft water is safe to drink often leads to confusion because the term applies to two different scenarios: water that is naturally soft due to its source, or water mechanically softened using a home treatment system. While naturally soft water is generally safe for consumption, water treated by a home softener introduces new considerations. These considerations are primarily related to its sodium content.
Defining Soft Water vs. Hard Water
Water is classified as hard or soft based solely on the concentration of dissolved divalent mineral ions it contains. Hard water is characterized by a high concentration of positively charged calcium and magnesium ions, which it picks up as it flows through rock and soil formations. These minerals cause visible scale buildup on plumbing fixtures and reduce soap lathering.
Soft water, conversely, has a low concentration of these dissolved minerals. Water that falls as rain, or sources that flow through mineral-poor granite or peat, are naturally soft. Hardness is often measured in grains per gallon (GPG) or parts per million (PPM); water containing less than 17 PPM of these minerals is typically classified as soft.
Is Naturally Soft Water Safe to Drink?
Water that is naturally soft from its source is safe to drink and poses no inherent health risks. This type of water, which is low in mineral content, is essentially the opposite of hard water. The absence of high mineral levels simply means the water has not traveled through geological areas rich in these compounds.
Some people have concerns about the lack of beneficial minerals in naturally soft water, but this is generally not a health issue. Most people receive the bulk of their daily calcium and magnesium intake from food, not from drinking water. The trace amounts of minerals in water contribute a small percentage to the overall diet, making the nutritional difference negligible for those with a balanced food intake.
How Water Softeners Change the Composition
The process most residential water softeners use to treat hard water is called ion exchange. This mechanism involves passing the hard water through a resin bed containing tiny beads coated with positively charged sodium ions. As the water flows over the resin, the divalent calcium and magnesium ions are attracted to the beads and are effectively swapped for the sodium ions, which are released into the water.
This exchange removes the hardness-causing minerals but introduces sodium to the drinking water. The resulting sodium level is directly related to the initial hardness of the water being treated. For every milligram of hardness removed, approximately two milligrams of sodium are added. The sodium added is often minimal, typically 20 to 40 milligrams per liter, but it can be a concern for certain individuals.
The primary safety consideration for softened water is its elevated sodium content, which can be an issue for people on sodium-restricted diets. Those with conditions like high blood pressure or kidney disease are often advised to limit sodium intake and should consult a physician regarding drinking softened water. For individuals with extremely hard source water, the sodium added could reach levels that warrant using a separate filtration system, such as reverse osmosis, for drinking and cooking.
Practical Reasons People Avoid Softened Water
People often avoid drinking softened water for practical reasons, the most common being taste. Softened water can taste “flat” because the minerals that give hard water a distinct flavor have been removed. The sodium introduced through ion exchange can also impart a slightly salty or metallic flavor.
Another practical concern, particularly in older homes, relates to plumbing. Soft water is more chemically aggressive and a more efficient solvent than hard water. This means it can more easily leach metals, such as copper and potentially lead from old solder or galvanized pipes, into the drinking supply. This increased reactivity makes soft water a risk factor for elevated heavy metal levels if the plumbing system is old or corroded.