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Water Conditioning Hardness

The hardness of water has traditionally been identified by the “soap” test. Hard water reacts with soap to form a precipitate (aka soap scum). This precipitation reduces the effectiveness of the soap and is seen as not being able to get the soap to lather with water as with washing your hands. Treated hard water, as with a water softener, will lather very easily since the ions that contribute to hardness are replaced with sodium or potassium as the water is treated.

Water hardness is primarily the quantitative measure of calcium and magnesium ions in water. In water, the total sum of the Ca2+ and Mg2+ ions is a parameter called "total hardness" which allows you to classify the degree of hardness of the water. Other ions are known that certain other ion species are known to contribute to the overall water hardness including iron, zinc, and manganese. The measure and subsequent control of water hardness is essential for detergents to work and to prevent scaling in plumbing and appliances.

Hardness is measured in grains per gallon (gpg) or milligrams per liter (mg/L). Water that is:

  • 0 to 1 gpg is considered soft
  • 3.5-7 gpg is moderately hard
  • > 7 is classified hard

Hardness in the forms of calcium, magnesium and total can also be measured by chemical test kits or photometrically with reagents. Photometric methods include reagent chemistries based on the Calmagite and EDTA colorimetric methods as found in the Standard Methods for the Examination of Water and Wastewater. Total hardness is an adaptation of EPA Method 130.1.









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