Causes and effects of hardness

Hardness is the property of water that prevents soap from lathering and causes scale in pipes and boilers. It is caused by dissolved salts of calcium and magnesium (and sometimes iron, strontium and manganese).

Causes

• Bicarbonates of Ca and Mg cause temporary (carbonate) hardness, which is removed by boiling.
• Sulphates, chlorides and nitrates of Ca and Mg cause permanent (non-carbonate) hardness.
• Water dissolves these salts when it passes through limestone, dolomite, chalk and gypsum rocks, so ground water is generally harder than surface water.

Effects

• Wastes soap, since hard water forms scum with soap before a lather forms; more soap and detergent are needed.
• Forms scale in boilers, hot water pipes, kettles and heat exchangers, reducing efficiency and sometimes causing explosion.
• Causes clogging of pipes and reduction of carrying capacity.
• Gives a bad taste and slows cooking (pulses and vegetables do not cook well).
• Harms textile, paper and dyeing industries; spoils the texture of clothes and can irritate the skin.
• Hardness is not seriously harmful to health; some studies even suggest that very soft water is linked to heart disease.

Hardness above 500 mg/l as CaCO3 is not acceptable; it is reduced by lime-soda softening or ion exchange.