Water Hardness

Hardness in water is the most common problem found with water extracted from sources under the ground and is different to brackish water which contains salt as a result of mixing with saline water such as from the sea. Hard water is water that contains dissolved hardness minerals above 17 milligrams per litre. These minerals are typically calcium, manganese and magnesium and sometimes other dissolved compounds such as bicarbonates and sulfates. Calcium usually enters the water as either calcium carbonate (CaCO3), in the form of limestone and chalk, or calcium sulfate (CaSO4), in the form of other mineral deposits. Magnesium usually enters the water as the mineral dolomite (CaMg(CO3)2).

Although there are numerous country-specific measures of harness in water the Degree of General Hardness (dGH) is more universal and is defined as 10 milligrams of calcium oxide per litre of water, or 17.848 ppm. However a single-number scale does not adequately describe hardness as the precise mixture of minerals dissolved in the water, together with the water’s pH and temperature determines the behaviour of the hardness. More exact measurements of hardness are obtained through a wet titration test and although water hardness usually only measures the total concentrations of calcium and magnesium, iron, aluminium, and manganese may also be present at elevated levels in some geographical locations. If Iron is present it will typically cause the calcification in the water to be a brownish rust colour instead of the usual white due to the oxide of the iron forming. Below is a table of approximate hardness concentrations to describe how hard water is.

Very soft: 0-4 dGH
Soft: 4-8 dGH
Slightly hard: 8-12 dGH
Moderately hard: 12-18 dGH
Hard: 18-30 dGH
Very hard: >30 dGH

Although hard water is generally not harmful to one’s health hardness in water becomes a problem when the water is to be used domestically for washing and heating water in geysers and kettles or in industry. The hardness minerals interfere with a particular process that can cause clogging of industrial equipment, inadequate control because of its lack of purity, or result in inferior products made with the water. Agriculturally, some plants are also more susceptible to extreme hardness in water and the hardness can clog up irrigation equipment. Hard water is also not as efficient or convenient as “soft water” in that you use only half as much soap cleaning with soft water. The hard water and soap also combine to form “soap scum” that can’t be rinsed off, forming a ‘bathtub ring’ on all surfaces and when it dries it can leave unsightly spots on clothes, crockery, glasses and eating utensils. The soap scum also remains on your skin after rinsing which clogs up the pores of your skin and coating hairs on your body, leaving you feeling sticky. This scum also provides ideal conditions for bacteria and yeast infections, causing thrush, nappy rashes and skin irritations that itch continuously. Furthermore, when hard water is heated, the hardness minerals dissolved in solution in the water re-crystallize and precipitate out to form hardness scale on heating elements and other surfaces. This scale can clog up pipes and heating equipment, causing premature failure, resulting in costly replacement.