You may have come across zeolites before; they are found in many washing powders in order to treat hard water, and are also used in water filter systems, to soften water, such as in dishwashers. Hard water contains Mg²⁺ and/or Ca²⁺ ions.  These ions react with soap to form ‘scum’.

In order to prevent the formation of ‘scum’ and allow the soap to lather, many washing powders contain zeolites to exchange the  Mg²⁺ and Ca²⁺ ions with Na⁺ ions, which do not prevent the soap from lathering. Hard water also produces solid deposits of calcium and magnesium salts, called ‘scale’ and can clog up pipes.