The U.S. Department of the Interior classifies hardness based on the concentration of grains per gallon (gpg) of calcium and/or magnesium. To put this in perspective. a typical aspirin equals about five grains of material. If the aspirin were dissolved in a gallon of water it would add 5 gpg of "aspirin" to the water.

The government classifies water as follows:

o soft (less than 1.0 gpg of calcium and/or magnesium)
o slightly hard (1-3.5 gpg)
o moderately hard (3.5-7.0 gpg)
o hard (7.0-10.5 gpg)
o very hard (greater than 10.5 gpg).

While hard water is not unhealthy, it does cause other problems:

Laundering

Soap curd (a sticky film formed when soap is used in hard water) influences fabric life and fading, according to a 1991 Purdue University study. The study indicated that fabrics washed in hard water tend to wear out up to 15 percent quicker than those washed in soft water, Colors also fade and whites darken more quickly when cleaned with hard water. In addition, laundry washed in hard water is more easily re-soiled.

Hard Water Scale

The minerals in hard water gradually settle, forming a hard scale surface. This scale eventually will clog pipes and can decrease the life of toilet flushing units by 70 percent and water faucets by 40 percent, according to a report published by the American Water Works Association (AWWA). The report also found that hardness scale shortens the life of washing equipment, dishwashers and clothes washers by as much as 30 percent.

Water Heater Efficiency

Hardness scale tends to form on the heating elements and heat transfer surfaces in water heaters. A 1981 study conducted by New Mexico State University determined that scale build-up can reduce a gas water heater's efficiency by as much as 29 percent, and an electric water heater's efficiency by as much as 21 percent. A study conducted by The Office of Saline Water, U.S. Department of the Interior, found that a water heater's useful life can be reduced by as much as 50 percent through scale build-up.

Cleaning Tasks

Soap curd makes cleaning and washing less effective and efficient. Greater physical effort and more cleaning agents are needed for surfaces such as floors, sinks and bathtubs. A comparison of hard and softened water sources for household use conducted by Ohio State University indicated that the time required for typical cleaning tasks was increased by almost 50 percent with hard water.

Soap curd film on the body can leave skin dry and hair dull and limp.

Streaks and Spotting

Soap curd formation can result in streaks, spots and film on glass and dishware.

The Water Softening Process

The negative effects of hard water can be reversed through the use of softened water. A water softener works on the principal of "cation exchange," in which ions of the hardness minerals are exchanged for sodium or potassium ions, effectively reducing the concentration of hardness minerals to insignificant levels. The exchange is accomplished in a tank, using a "resin" of tiny beads made from a special plastic material.
After a period of use, the sodium or potassium ions are completely exchanged and the unit has to be "backwashed" or "regenerated." This requires the use of sodium or potassium chloride, which is loaded into a "brine tank" and dissolved to form a briny liquid used to recharge the system. There are three types of water softeners:

Automatic

An automatic water softener is equipped with a timer, which starts the regeneration process at preset intervals. This usually occurs when water use is minimal, such as the early morning hours.

Demand Initiated Regeneration (DIR)

Instead of regenerating at a preset interval, DIR units use sensors or meters to regenerate when soft water runs out. Because they adjust to the amount of water actually used, DIR units consume up to 50 percent less salt and water than preset automatic softeners.

Portable Exchange

A portable exchange unit is a type of softener with a removable resin tank. When the resin material in the tank is exhausted, a fresh tank is installed and the used tank returned to a central plant for regeneration.