Hard and Soft Water

Water hardness is determined by the level of certain metallic ions like calcium and magnesium in the water.
Hard water contains high concentrations of calcium and magnesium ions whereas soft water contains few or no such ions.
Temporary hardness is due to the presence of hydrogencarbonate ions (HCO3-) which can be removed by boiling.
Permanent hardness is due to sulfate or chloride ions and cannot be removed by boiling.

Formation of Hard Water

Hard water forms when water passes through or over calcium or magnesium compounds such as limestone and gypsum.

The temporary hardness in water can be removed by boiling to form scale, or solid deposits of calcium carbonate.
The permanent hardness in water cannot be removed by boiling but can be treated using chemicals or by a process known as ion exchange.

Soap is less effective in hard water, forming an insoluble residue or ‘scum’ instead of lather.
Hard water can lead to the accumulation of lime scale in kettles, heaters and pipes, which can decrease the efficiency of heating systems and shorten their lifespan.
However, consuming hard water can provide necessary minerals for a healthy diet and is associated with lower incidence of cardiovascular diseases.

To soften hard water, substances such as washing soda (sodium carbonate) can be used, which precipitate the calcium or magnesium ions as carbonate.
An appliance such as an ion-exchange column or water softener can be used to soften hard water by exchanging calcium and magnesium ions for sodium ions.
The ion-exchange resin in the column needs to be periodically regenerated with a solution of sodium chloride (common salt).

##Differentiating between Hard and Soft Water

With soap, hard water doesn’t effectively form lather while soft water forms lather easily.
A titration method using a standard soap solution can quantitatively determine the hardness of the water.
A precipitate forms when you add soap to hard water, unlike with soft water.