"Hard" water is rich in dissolved mineral deposits, particularly calcium and magnesium. While hard water doesn't pose a health risk, calcium and magnesium interfere with the suds action in soaps and detergents. Additionally, mineral deposits or scaling can build up and affect water pipes and fixtures. Many softening agents such as borax and washing soda have historically been added to soften water. But, there are other household chemicals that are effective treatments as well.
Sodium-based salts are commonly used with water softening systems to treat hard water. As a coating on synthetic beads called "zeolites," sodium ionizes in solution and trades places with calcium and magnesium in what's called an ion-exchange procedure. Once calcium and magnesium ions bind with the zeolite, sodium, a softer ion remains in solution. While salt-based chemicals are effective at softening water, many municipalities restrict the release of softened water into the public water system. Though not as saline as salt water, softened water can kill plant and aquatic life; and, for those with high blood pressure or low-salt diets, softened water can cause additional health risks if used for consumption.
Potassium-chloride is a sodium-free chemical used in water softening systems. According to Morton Salt, a manufacturer of salt-based products, use of potassium chloride as a water softener can reduce sodium in water systems by 99 percent. Additionally, it can serve as a source of potassium, an essential nutrient. However, an article published in the New England Journal of Medicine cautions that patients with renal failure and hyperkalemia can suffer complications by drinking potassium-softened water. In hyperkalemia, the potassium in the blood exceeds normal levels. Since these patients are normally counseled to reduce or avoid potassium-rich foods, they should avoid potassium-softened water.
Historically, washing soda was added to wash water as a cleaning booster. A crystalline form of sodium bicarbonate, washing soda added to hard water replaces calcium ions with sodium in a chemical reaction. While unsuitable for use in drinking water, it does improve suds action when added to laundry detergents.
Like washing soda, borax or sodium borate, softens water by binding with calcium and magnesium ions. According to the Water Research Center, hard water minerals reduce the effectiveness of soaps and detergents. Borax acts as a detergent booster. However, borax, like washing soda is toxic when consumed and should not be used to soften drinking water. Additionally, because it can cause skin irritations, it's not suitable for bathing.