The presence of Iron in drinking water gives an earthy taste and can discolour the water. Washing may also be discoloured and some staining of sanitary ware may occur. Manganese can also cause discolouration of washing and staining of sanitary ware. It will also give a bitter taste.

Iron and Manganese can be removed with a catalytic filter media which uses Oxygen in the water to convert the metal ions from the soluble form to an insoluble form. This insoluble precipitate is then filtered out onto the surface of the media.

To remove accumulated deposits from the filter bed, the water flow through the filter is reversed (backwashed). This process is automatically controlled by a time clock. The type of unit will depend on the level of contamination. Units are tailored to specific requirements.

Some water supplies are acidic. Whilst not harmful to health, this will cause damage to metallic pipes, giving characteristic blue staining in wash basins etc. People with light coloured hair may also experience a greeny blue tinge to their hair after washing. Acidic
water should not be used in lead pipes.

Water is passed over a filter bed of Dolomitic limestone or similar material, which bring the water back to a pH of 7. If the water does not contain significant levels of Iron and Manganese a backwash head will not be required. The level of filtration medium requires topping up periodically.

Hard water causes scale which reduces heat transfer efficiency in water systems; it also causes high detergent use in domestic and catering settings.

An ion exchange system is used to remove the
calcium and magnesium from the water. The process is low cost, requiring only salt
to run it.

EEC permitted maximum concentration is 50mg per litre, with an advisory maximum of 25mg per litre. Nitrate needs to be reduced by ion exchange in a filter bed similar to a softener.

This can be done on either a large scale (point of entry) or, for drinking purposes, with a small unit at point of use.