PA Environment Digest

Hard water can make deposits on dishes and faucets, cause dingy laundry, and diminish the effectiveness of appliances that heat water. The science of hardness and the mechanics of the ion exchange water softener are explained.

Depending on where you live in Pennsylvania, you may have hard water, and you may know this from a recent water test, or just from characteristics of your water that indicate that the hardness is present. If your water is considered to be hard, this means that it contains a higher amount of two minerals, calcium and magnesium.

These minerals do not cause any adverse health effects and are actually important to our bodies. The trouble occurs when the minerals build up on fixtures and appliances causing them to not work as well as they used to, or when they decrease the effectiveness of soaps and detergents and give light-colored laundry a dingy look.

Water hardness is expressed in one of two units of measurement. The first unit is parts per million (ppm) of calcium carbonate, a term equivalent to the concentration of dissolved calcium and magnesium. One ppm means that one unit of calcium carbonate is dissolved in one million units of water.

Parts per million is the same as milligrams/liter (mg/l). A second expression of hardness is grains per gallon of calcium carbonate. A gpg is used exclusively as a hardness unit and equals approximately 17 mg/l or 17 ppm.

If you have your water tested, the report will use one or both of these units to tell you how hard your water is. A gpg reading of more than 7.0 is considered hard, while a ppm reading of more than 120 indicates hard water.

If you choose to remedy your hard water, the most typical way to accomplish this is through use of a water softener, which is an ion exchange unit. The ion exchange works by filtering the water through an exchange media known as resin or zeolite. Typically, the resin is a synthetic or natural, sand-like material coated with positively charged sodium ions.

As the calcium and magnesium dissolves into positively charged ions, an ion exchange environment is created. The water flows through the unit while the resin releases its sodium ions by trading them for the calcium and magnesium ions. The water flowing out of the device is now soft since it no longer contains calcium or magnesium. The resin will periodically need to be soaked with a salt solution to reestablish the sodium ions. The process for doing this is called backflushing or backwashing.

If you or someone in your household is on a low sodium diet, potassium chloride may be used in place of sodium chloride to achieve soft water without the added sodium.

For more detailed information on water softening, you may want to consult Penn State’s Water Resources Fact Sheet about Water Softening.

(Written by: Susan Boser, Extension Educator, Penn State Extension, reprinted from the Penn State Extension Watershed Winds newsletter.)

Share this: