Presence of calcium and magnesium ions (polyvalent ions) are what cause water hardness. The geographical location of the water source plays a major role in determining the source of water hardness. In limestone areas, for example, calcium is the major source of water hardness. Carbon dioxide dissolved in water causes the water to turn acidic and when calcium is introduced, especially from limestone areas, calcium carbonate is formed. Calcium carbonate is responsible for scaly deposits on utensils such as kettles. Magnesium is abundantly found in rivers and seawater. In seawater, magnesium is the second most abundant mineral after sodium.
The type of salt dissolved in the water determines whether water has permanent or temporary hardness. Hydrogen-carbonate salts of magnesium and calcium cause temporary hardness, while chlorides and sulfates of magnesium and calcium cause permanent hardness. Simply heating water removes temporary hardness, while permanent hardness requires more complex chemical means.
When washing with hard water and soap, formation of scum occurs due to a chemical reaction between the dissolved mineral causing hardness and soap compound. The term water hardness was coined from the difficulty of hard water to lather with soap; instead, scum is formed as a result. Washing with hard water is disadvantageous. For instance, scum formed with soap stuck in fabric can make it stiff.
Pure water is neutral in nature therefore it is at the pH 7 mark on the pH scale. pH values greater than seven mean the compound is basic while the opposite indicates acidity. For water, pH levels greater than 8.5 could mean the water is hard due to the dissolved minerals in it.
Ridding water hardness is mostly done for water used in areas where this water property is unwanted such as industrial areas and areas where hard water interferes with washing and bathing. Eliminating water hardness may involve a number of processes including boiling, use of slaked lime and washing soda or through an ion exchange process.