Water hardness

Drinking water

Safe drinking-water is defined by the ‘Guidelines for Drinking-water Quality’ from the WHO (World Health Organisation).

Safe drinking-water according to a.m. Guidelines does not represent any significant risk to health over a life-time of consumption, including different sensitives that may occur between life stages. E.g. risks of waterborne diseases which concerns infants and young children, people living under unsanitary conditions and the elderly.

The Guidelines are also applicable to packed water and ice intended for human consumption.

The form and nature of drinking-water standards may vary among countries and regions. The aim of the Guideline is to support the development and implementation of risk management strategies. To ensure the safety of drinking-water. These strategies may include national or regional standards developed from the scientific basis provided in the Guidelines (e.g. chlorine as additive). The Guidelines describe reasonable requirements of safe practice to protect the health of consumers.

Everyone has experienced red eyes after going swimming. They are caused by chlorine, which is in the swimming pool water as a disinfectant.

Drinking water from domestic taps

The quality of domestic drinking water can be affected the material pipelines are made of, by the amount of time the water was in the pipes and temperature. More information on this under “Contaminants”.

Every three years, the European Commission collects data from larger drinking water plants. The data helps control whether drinking water complies with European guidelines and whether maximum permissible values are respected. Water works that supply more then 5.000 residents are affected by these controls.

Water hardness

Thus term is often used in connection with drinking water. Normal drinking water from the tap and water as it is found in nature contain dissolved gases and salts, like calcium and magnesium salts, amongst other substances.

These salts are called “hardness minerals“, their concentration in water is known as “water hardness“. Hardness minerals tend to form insoluble compounds like lime (calcium carbonate). Calcium carbonate is a compound made of calcium hydroxide and carbon dioxide.

How does water hardness develop?

Most drinking water derives from ground water. It is constantly re-created by draining rain water.

Rain water contains a portion of dissolved carbon dioxide, as the gas is absorbed from the atmosphere by the water. Carbon dioxide that is dissolved in water creates carbonic acid. The carbonic acid content loosens mineral compounds whilst the water trickles through the soil, stones, rock formations and rubble.

In regions where sand and limestone prevail, the water is harder. Rain and spring water is softer in areas where the primary rocks are hard (granite, basalt), as only few mineral compounds can be loosened from the rocks.
As calcium and magnesium reduce the washing efficiency of detergents, more cleaning agents must be used in areas with high water hardness or less in areas with softer water, respectively. Of course this counts for the durability of water filter cartridges, too. The softer the water, the more one cartridge can filter.

Soft water can attack the material water pipes are made of, yet protects appliances. Soft water is more appropriate for watering indoor plants and washing/ washing up.

The travertine terraces in Plitvice/Croatia are a good example for extreme calcification. Here, the water trickling down from the hills absorbs so much lime, that terraces of lime scale form on the way downhill. Stalactite caves are other examples.

The lakes of Plitvice – the result of calcification

In the house, this phenomenon can be observed in form of unattractive scale around dripping taps or in all kitchen appliances in which water evaporates or is heated, for example coffee machines, electric kettles, steam irons etc.

In the first half of the past century, synthetic detergents that do not react with water hardness, as we know them today, did not exist. In order to save expensive soap when washing, soda was used to make the water less hard. Three containers with soda, soap for washing and sand to scrub with were found in every kitchen.

Hard water through heating up and „acid rain“

If water is heated, the equilibrium between lime and carbonic acid may be disturbed. The absorption of lime (like when rainwater trickles through rock formations) takes place in the opposite direction and solid lime scale is deposited. These unwanted deposits found in electric kettles and coffee machines, for example, are known as “scale”.

Rainwater has a hardness degree of zero. Yet rain or other forms of precipitation can also form acids through sulphuric acid. For example, when sulphurous fossil fuels like petroleum or coal are burnt. This can also lead to an increase in the hardness degrees.

The hardness degree of ground water can rise through areas that are intensively cultivated agriculturally. During fertilisation, the contained nitrogen is transformed and through a certain process becomes nitric acid. This nitric acid releases hardness minerals from lime (if present) and clay minerals. That is why agriculturally cultivated areas can become acidic. Dunging with lime can prevent the soil from becoming acidic and keep it fertile. Large areas of forest are also dunged with lime with the help of helicopters.

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