The hardness or softness of water depends on the amount of calcium in it – the more it contains, the harder the water is.

When rain falls it contains no calcium but, as it flows over the land and percolates through rocks, it dissolves minerals and becomes harder.

The amount it picks up depends upon the geology of the area and the hardness of water varies widely throughout the country.

Here, in southern England, much of our water is collected from underground chalk aquifers where the water is hard.

The definition of water hardness is based on the amount of calcium it contains per litre.

• Soft water contains less than 30mg of calcium per litre
• Moderately hard water contains between 30 and 60mg
• Hard water between 60 and 120mg and
• Very hard water contains more than 120mg of calcium per litre

The average hardness in your water source can be found by entering your postcode in the "Where I live" section on the right.

There is no UK or European standard set for the hardness of drinking water. Southern Water does not soften water at any of its treatment works.

The degree of hardness does not affect the quality of the drinking water.

While hard water does not produce as much lather this has no effect on the performance of soaps and washing detergents.

Modern dishwashers have built-in water softeners that prevent white deposits or spots forming and water softening products can be added to older machines.

When hard water is heated harmless limescale is formed. Regular cleaning of kettles will prevent the “scum” floating to the surface, while keeping the temperature of the hot water systems below 60°C will reduce the formation of limescale in boilers, on heating elements and in hot water pipes.

Find out more information on limescale.

Alternatively it can be avoided by installing a household water softener.

Water softeners must be fitted to comply with the Water Supply (Water Fittings) Regulations 1999. Find out more information about Water Regulations.

If you had a water softner installed it is essential to have one tap supplying unsoftened water for cooking and drinking, because softeners can significantly increase the level of sodium in water.

Looking after water in your home.*

* Southern Water is not responsible for content on external websites.