What is Hard Water?

Causes & Effects of Water Hardness

Hard water reduces the effect of soap and detergent and causes limescale build-up, but provides a useful source of calcium and magnesium. What softeners are available?

When water is referred to as “hard” or “soft”, it is the number of dissolved minerals that are being described. Tap water in different geographical areas seems to have different properties, especially relating to the effect of detergents, and to the quantity of limescale produced in household appliances.

Dissolved Minerals

The water in rivers, lakes, or under the ground, as well as the water that comes out of the tap, is not pure water, there are small amounts of other chemicals dissolved in it. Some of these chemicals come from the rocks and soils that the water has passed through since it has fallen from the sky like rain. Rainwater is slightly acidic because it has some carbon dioxide dissolved in it, so when it passes through rocks containing calcium carbonate, calcium sulfate, or dolomite (calcium magnesium sulfate), some of these compounds are dissolved into the water.

Caused by Limestone and Chalk

This means that water from areas where there is a lot of limestone (containing mostly calcium carbonate, but also dolomite) or chalk (even higher quantities of calcium carbonate), has a lot of calcium, magnesium, carbonate, hydrogen carbonate, and sulfate ions present in the water – making it hard water. Areas, where there are no limestone or chalk rocks, have much fewer dissolved minerals, and so the water in these areas is called soft water.

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Disadvantages of Water Hardness

It is easiest to identify water hardness by its effect on soap and other detergents. Because soaps and detergents have an ionic nature, when they are dissolved in hard water, each soap molecule reacts with calcium ions, to produce scum. This essentially renders the soap useless, and much more soap or detergent is required to clean anything if used with hard water.

Another major problem with hard water is that, when it is heated, in a kettle, washing machine, or hot water pipe, it begins to deposit solid calcium carbonate. This is the cause of limescale building up in kettles, damaging heating elements of washing machines, and blocking water pipes.

Advantages of Water Hardness

Hard water does have some advantages, however. It is an important source of calcium for teeth and bones, as well as other minerals necessary for healthy living. It also does not dissolve so many undesirable substances, so its use to make beer and other beverages produces better results.

Water Softeners

To reduce the negative effects of hard water, many ways have been developed to remove hardness. These techniques range from adding softening chemicals to laundry in order to avoid having to use large quantities of detergent. Portable filters can be used to filter water used in kettles, to prevent scale build-up on the heating element.

Water softeners work using a technique called ion exchange, whereby calcium and magnesium ions are replaced by sodium ions, which do not cause hardness. More recently magnetic water conditioners have been developed which use a magnetic field to alter the way the calcium and magnesium ions behave, reducing the formation of scale.

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