Page 38 - Curriculum Visions Dynamic Book

Hard water
There are many compounds dissolved in water. Just as invisible bugs in water can cause great health problems, so invisible chemicals can cause a range of problems for people.
Calcium and magnesium compounds are commonly found in water supplies. If water supplies contain more than 120 mg of calcium and magnesium compounds in each liter of water, the water is described as hard water.
Do you live in a hard-water area?
Most people have a rule of thumb for telling if they live in a hard-water area: if they
have trouble getting soapy when in the bath or the shower, then they know they are in a hard-water area.
Most people who live in limestone areas have hard-water supplies, but because water is often transferred for hundreds of kilometers, to match supply and demand, areas far from limestone rocks can also have hard water.
Limescale
Calcium and magnesium carbonates are together usually referred to as limescale.
You can sometimes see the thin form of these carbonates build up (precipitate) in many places where hot water is used, such as around the hot water tap in a bathroom, where it gives white smears that thicken to give a dull film.
Carbonates also precipitate quickly on the heating element or side of a coffee jug or electric kettle, because bicarbonates are not stable
in hot water.
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 You know you are in a hard-water area if scale forms on a boiler or kettle element quickly and looks like this.
Also...
Hard water can be either temporary or permanent. Water containing soluble calcium hydrogen carbonate (calcium bicarbonate) is temporarily hard because calcium hydrogen carbonates can be removed by boiling (carbonate precipitates). Water is permanently hard if it contains calcium or magnesium salts other than the calcium hydrogen carbonates, as these cannot be removed by boiling.
It does not produce scale in kettles but it does make it difficult to obtain a lather with soap.