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During the softening process, sodium is released from the exchange media into the output water. It is achieved either by adding chemicals that form insoluble precipitates or by ion exchange. Home water softeners usually work similarly and consist of zeolite or another ion-exchange resin in a tank connected directly into the water system. Hard water can be problematic because the calcium and magnesium ions react with the higher fatty acids of soap to form an insoluble gelatinous curd, thereby causing a waste of the soap (this objectionable reaction does not take place with modern detergents). By signing up for this email, you are agreeing to news, offers, and information from Encyclopaedia Britannica. Premium Membership is now 50% off! Hardness is measured by the level of calcium and magnesium bicarbonates in water and together represent Total Hardness (TH). Hard water is generally not harmful to one's health but can pose serious plumbing problems in both residential and commercial applications. These ions enter a water supply by leaching from minerals (such as limestone) within an aquifer. Eliminating or reducing water hardness is done with a piece of equipment known as a water softener. Ion exchange resins can be manufactured to selectively prefer one, or perhaps several different types of ions. Mostly it has to do with elevated levels of calcium and magnesium, which can make it difficult for products like soap to dissolve in the water. The presence of iron characteristically confers a brownish (rust-like) colour to the calcification, instead of white (the color of most of the other compounds). Omissions? The following equilibrium reaction describes the dissolving/formation of calcium carbonate scales: Calcium and magnesium ions can be easily removed by the ion exchange process. Although water hardness usually measures only the total concentrations of calcium and magnesium (the two most prevalent divalent metal ions), iron, aluminum, and manganese can also be present at elevated levels in some locations. This process continues until the resin becomes saturated with hardness ions and depleted of sodium ions. For every grain of hardness removed from water, 8 mg/1 (ppm) of sodium is added. A softener is comprised of different components, each having their own unique purpose. A third type of control uses a mechanical water meter to measure water usage and initiate recharging. The salt or potassium chloride is a sacrificial media and must be replenished on a regular basis to ensure adequate softening form the device. Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox. Corrections? This article was most recently revised and updated by, https://www.britannica.com/technology/water-softening. 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