Testing for hardness.Apps Laboratories home.
Hardness is a measure of mainly calcium and magnesium in water. By convention hardness is given as amount of CaCO3 although it actually includes magnesium. Hardness affects fish health in aquaculture, flavours in beverage manufacture and scale buildup where water is used in heating. Hardness in irrigation water can help offset the undesirable effects of sodium on plant nutrition and soil structure. Hardness comes from the contact water has with minerals in rocks and soil.
The calcium and magnesium associated with or in balance with bicarbonates in water is called temporary hardness or carbonate hardness. When water warms, carbon dioxide becomes less soluble and some is driven out of solution. This represents a loss of acidity because the carbon dioxide normally forms carbonic acid - the acid that dissolves the carbonates in the first place. To balance this loss some of the bicarbonate ions recombine with calcium and magnesium ions in solution and form insoluble precipitates of calcium and magnesium carbonate. Permanent hardness is calcium and magnesium that originated from chlorides and sulphates.
For more information please see What_do_you_water_test_results_mean.doc.