Hardness

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, to prevent scaling in boilers and cooling towers, and for basic home use.

Hardness in the forms of calcium, magnesium and total can also be measured photometrically with reagents. Photometric analysis is based on the Beer-Lambert principle of absorbance. Photometric analysis products include handheld chemical test kits, colorimeters, portable and benchtop photometers, and spectrophotometers. 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.

Hardness is commonly expressed as mg/L of calcium carbonate (CaCO3). The portable and benchtop photometers allow hardness to be expressed as French degrees (of), German degrees (odH) and English degrees (oE). For water conditioning companies the chemical test kit can measure as grains per gallon (gpg).