Hard water contains dissolved salts such as magnesium and calcium carbonates , bicarbonates or sulphates . It is difficult to produce lather from soap with hard water and an insoluble scum is formed . The metal ions Ca+2  and Mg+2 react with the stearate  before any lather is produced . Hard water also produces scale in water pipes, boilers , and kettles

Temporary hardness 'is due to the presence of Mg(HCO3)2 and Ca(HCO3)2 . It is called temporary because it can be removed by boiling , which drives off CO2 and upsets the equilibrium

Permanent hardness is not removed by boiling and is due to MgSO4 or CaSO4 in solution . small quantities of pure  water are prepared in the laboratory either  by distilling the water or by passing it through an ion-exchange resin