Chemistry in your cupboard

Tap water

In the western world, we think of our tap water as being pure. And it is in the sense that it is safe to drink and contains no dangerous micro-organisms - viruses and bacteria - which could make us ill. However, in the chemical sense of being a single substance, it is not pure at all. It will contain materials dissolved from the ground, through which it has seeped between falling as rain (when it has effectively been distilled) and arriving in a reservoir from which it enters the distribution system.

These dissolved materials can make a great deal of difference to water's ability as a cleaning solvent - for its use in washing machines and dishwashers, for example. Water containing dissolved minerals is termed ‘hard’ and water softeners such as Calgon® may be used to reduce the effects of this and improve cleaning.

Hard water has two effects on the cleaning efficiency of washing machines and dishwashers. Firstly, inorganic compounds may deposit on the electric elements used to heat up the cleaning water, thereby reducing efficiency. These compounds may also deposit on the articles being cleaned. Secondly, metal ions in the hard water react with soap and certain other detergents to form scum, which reduces cleaning power, and deposits on the items to be cleaned. The solution to these problems is to use more cleaning agent.

This is why laundry detergent manufacturers recommend different levels of detergent depending on the water hardness: the higher the water hardness, the more detergent is required, see Figure 1.

Figure 1: Manufacturers recommend using more detergent in hard

The use of a water softener can reduce the amount of detergent required by up to 40%.

The taste of water

Dissolved materials also make a significant difference to water's taste. If you live in a hard water area, you may never have tasted pure water. If you get the opportunity to taste some distilled or deionised water at school, college or elsewhere try it (with suitable hygiene precautions). You may be surprised.

Note: Do not taste water that has been treated with Calgon® or other water softening products.