People who live in parts of the country founded on chalky or limestone rock, and who have local water piped into their homes, end up with some of the rock in their kettles.

When rainwater percolates through a chalky landscape, it slowly dissolves away some of the mineral. When the water is boiled, the chalk comes out of the solution and sticks to the sides of the kettle as lime scale, or kettle `fur’.

Water that is laden with chalk and lime (both of them forms of calcium) makes its presence felt in another way. You cannot get much of a lather when you wash in it with soap. Instead of lathering, the water reacts with the soap chemicals to form an insoluble scum. It is described as ‘hard’. Lime-scale stains also occur on baths and lavatories and around the outlets of taps. The lime scale can be removed with proprietary descalers. A common type uses a concentrated solution of formic acid.

The acid dissolves the lime scale, making it fizz as carbon dioxide gas comes off.

The lack of a good lather in hard water is less of a problem than it used to be because modern detergents form no scum.

In some boilers and hot-water systems hardness can be more than a nuisance. The lime scale clogs up pipes and reduces the water flow. In boilers the scale forms a barrier that prevents the efficient transfer of the heat, leading to much higher heating bills. So, particularly in industrial plants, water needs to be softened before it enters hot-water systems.

Many waterworks remove hardness by chemical methods, such as treatment with slaked lime and soda ash, before pumping the water to houses and factories.

The beauty of lime scale Flower-shaped crystals of calcium carbonate¬† loch their ‘petals’ together to form the lime scale which causes a hard deposit on the inside of a kettle or boiler. Stalactites, which hang from the ceilings of limestone caves, are massive lime-scale structures.