Water Softening or Ion Exchange

Water softening to condition hard water is perhaps the most familiar water conditioning system known to consumers. Hard water is caused by calcium and magnesium that are dissolved in the water. This causes scale to form in hot water pipes and water heaters. It interferes with the cleaning action of soaps and detergents, and forms a film on skin, clothing and fixtures. Hardness is measured either as milligrams per liter or parts per million. However, it is normally expressed in grains of hardness per gallon of water. The table lists the relative hardness of water expressed in both forms.

Softeners also will remove small amounts of iron and manganese if they are in a soluble or ferrous form.

The most common way to soften water is the cation-exchange water softener. A synthetic resin with a strong attraction for calcium, magnesium and other positively charged metal atoms called "cations" is saturated with sodium from a salt solution. As water passes through the resin, the sodium exchanges with the calcium and magnesium. Eventually, so much hardness collects on the resin that the unit can no longer soften the water and recharging is necessary. Then, the softening material is backwashed with a brine solution to replace the sodium and enable the ion exchange process to continue.

The major disadvantage of water softeners is that they remove beneficial calcium and magnesium and substitute sodium. People who are on a restricted sodium diet may be advised not to drink softened water. To overcome the problem, soften only the hot water tank lines, leaving the major cold water line for drinking unsoftened water. Softened water is more corrosive than unsoftened water, and the waste brine may be a disposal problem. Softening systems range from $650 to $2,100.

Source: University of Georgia
Prepared by: Dale Dorman, Extension Housing Specialist
http://www.engr.uga.edu/service/extension/publications/c819-10c.html