Is Hard Water Dangerous to Drink?

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By Ada McVean BSc.

Reprinted with permission of McGill University's Office for Science and Society. The original article can be found here


What is Hard Water?

Hard water is water containing high concentrations of dissolved minerals, usually calcium or magnesium carbonates (CaCO­or MgCO3), chlorides (CaCl2or MgCl2) or sulphates (CaSO4or MgSO4). The hardness of water depends on its source. Groundwater that has been in contact with porous rocks containing deposits of minerals like limestone or dolomite will be very hard, while water from glaciers or flowing through igneous rocks is much softer.

The hardness of water is determined by the milligrams of calcium carbonateper litre and is reported it in parts-per-million (ppm). In general, water with less than 60 ppm can be considered soft, water with 60-120 ppm moderately hard, and water with greater than 120 ppm hard. For reference, Montreal’s water is typically around 116 ppm, or moderately hard, and sea water’s hardness is approximately 6,630 ppm since it contains many dissolved salts (depending on the sea, of course).

Hard water can interfere with the action of soaps and detergents and can result in deposits of calcium carbonate, calcium sulphate and magnesium hydroxide (Mg(OH)2) inside pipes and boilers, causing lower water flows and making for less efficient heating. The ions in hard water can also corrode metal pipes through galvanic corrosion. Water softening filters can circumvent these problems through the use of ion-exchange resins that replace calcium and magnesium ions with sodium and potassium ions. But if one consumes water with higher-than-average concentrations of calcium and magnesium. Is that OK?

The Health Effects of Hard Water

Studies have generally found hard water to have positive effects on the health of its drinkers. Several studies have reported that calcium and magnesium in drinking water have a dose-dependent protective effect when it comes to cardiovascular disease. There is also some evidence that calcium and magnesium in drinking water may help protect against gastric, colon, rectal cancer, and pancreatic cancer, and that magnesium may help protect against esophageal and ovarian cancer. Hard water may also serve a protective role against atherosclerosis in children and teens.

Some studies have shown a relationship between the mineral content of water and eczema or dermatitis in children. However, a 2011 study from the University of Nottingham involving 336 children aged 6 months to 16 years with eczema put that relationship to the test. The researchers installed water softening units in half of the participants’ homes and monitored the children’s eczema over a period of 3 months. Using a standard scoring system, the group that received softened water showed a 20% improvement, while the group that continued with hard water showed a 22% improvement, making it unlikely that hard water is contributing to worsening eczema symptoms.

Likewise, while some studies have shown correlations between water hardness and kidney stone formation, the majority of studies have found no such relationship.

It is estimated that individuals living in hard water areas who drink 2 litres of water a day ingest about 52 mg of magnesium from their water. Considering the daily recommended intake of magnesium is 420 mg, water can account for about 12% of that.

Individuals with type 2 diabetes often experience hypomagnesemia (low magnesium) as insulin regulation requires magnesium to function. In these people, the extra intake of magnesium through drinking water could be beneficial. The heightened magnesium concentration in hard water can also benefit people experiencing chronic constipation, as magnesium salts act as laxatives. One study noted that vegetables cooked in hard water often show an increase in their calcium concentration, as opposed to the decrease seen when they’re cooked in soft water.

It is fairly difficult for humans with healthy kidneys to experience hypercalcemia (too much calcium), as any excess calcium is excreted through the kidneys. Similarly, hypermagnesemia is fairly rare, and usually just results in short episodes of diarrhea.

The Physical Effects of Hard Water

There are, however, some non-medical reasons hard water isn’t always preferable. Hard water can appear cloudy if the solubility of mineral salts is exceeded. Furthermore, if the calcium concentration surpasses 100 ppm, the water will taste “funny.” Neither of these presents a risk, but consumers prefer a “clean” appearance and taste.

Basically, while hard water can be hard on appliances and pipes, it is not hard on the body, and can actually give the daily intake of calcium and magnesium a nice little boost.