Chlorine is the 18th most abundant of the earth's 92 natural elements. It was first harnessed industrially more than 100 years ago and became a cornerstone of the chemical industry's post-World War II expansion. 60% of western European chemical industry sales are attributed to products that either contain chlorine or were produced with its help. Industrial manufacture of chlorine is achieved by electrolysis -- passing an electric current through brine, saturated salt water. This breaks the brine up into its component parts hydrogen, chlorine and caustic soda. More than 9 million tonnes of chlorine and a similar quantity of caustic soda are produced annually in western Europe. Almost 2 million jobs in Europe are related to chlor-alkali production.
Common tap water is often high in chlorine, which has been found to destroy friendly intestinal bacteria.