The hardness of water is the sum of concentrations of calcium and magnesium that exist in water. Hard water forms in water flowing through limestone, chalk or gypsum deposits composed mainly of carbonates, bicarbonates and sulphates of calcium and magnesium.
It is one of the most studied and named parameters when talking about the WATER QUALITY.
WHY WATER HARDNESS IS IMPORTANT
The calcium and magnesium ion content is important,
HARD/SOFT WATER VALUES
HOW WATER HARDNESS IS MEASURED
MEASURING WATER HARDNESS
Water hardness is the traditional measure of the capacity of water to react with soap,
hard water requiring considerably more soap to produce a lather. Hard water often
produces a noticeable deposit of precipitate (e.g. insoluble metals, soaps or salts) in
containers, including "bathtub ring". It is not caused by a single substance but by a
variety of dissolved polyvalent metallic ions, predominantly calcium and magnesium
cations, although other cations (e.g. aluminium, barium, iron, manganese, strontium
and zinc) also contribute. Hardness is most commonly expressed as milligrams of
calcium carbonate equivalent per litre. Water containing calcium carbonate at
concentrations below 60 mg/l is generally considered as soft; 60-120 mg/l,
moderately hard; 120-180 mg/l, hard; and more than 180 mg/l, very hard (McGowan,
2000). Although hardness is caused by cations, it may also be discussed in terms of
carbonate (temporary) and non-carbonate (permanent) hardness
Hard drinking water may have moderate health benefits. It can pose critical problems in industrial settings, where water hardness is monitored to avoid costly breakdowns in boilers, cooling towersand other equipment that handles water. In domestic settings, hard water is often indicated by a lack of foam formation when soap is agitated in water, and by the formation of limescale in kettles and water heaters. Wherever water hardness is a concern, water softening is commonly used to reduce hard water's adverse effects.
EXCESS CALCIUM AND MAGNESIUM INTAKE
To a great extent, individuals are protected from excess intakes of calcium by a tightly regulated intestinal absorption and elimination mechanism through the action of 1,25-dihydroxyvitamin D, the hormonally active form of vitamin D. When calcium is
absorbed in excess of need, the excess is excreted by the kidney in healthy people
who do not have renal impairment. Concern for excess calcium intake is directed
primarily to those who are prone to milk alkali syndrome (the simultaneous presence
HARDNESS IN DRINKING-WATER
of hypercalcaemia, metabolic alkalosis and renal insufficiency) and hypercalcaemia.
Although calcium can interact with iron, zinc, magnesium and phosphorus within the
intestine, thereby reducing the absorption of these minerals, available data do not
suggest that these minerals are depleted when humans consume diets containing
calcium above the recommended levels. For example, even though high intakes of
calcium can exert acute effects on iron absorption, there is no evidence of reduced
iron status or iron stores with long-term calcium supplementation.
The major cause of hypermagnesaemia is renal insufficiency associated with a
significantly decreased ability to excrete magnesium. Increased intake of magnesium
salts may cause a temporary adaptable change in bowel habits (diarrhoea), but seldom
causes hypermagnesaemia in persons with normal kidney function. Drinking-water in
which both magnesium and sulfate are present at high concentrations (above
approximately 250 mg/l each) can have a laxative effect, although data suggest that
consumers adapt to these levels as exposures continue. Laxative effects have also
been associated with excess intake of magnesium taken in the form of supplements,
but not with magnesium in diet.