Ion exchange units replace calcium and magnesium ions from water are known as water softeners.

They may also remove varying amounts of other inorganic pollutants such as metals, but they wll not remove organic chemicals, pathogens, particles or radon gas.

Water softener units work most efficiently with particulate free water.

Principles of Ion-Exchange to soften water:

Calcium and Magnesium ions are atoms having a positive electrical charge, as do sodium and potassium ions.

Ions of the same charge can be exchanged.

This "exchange or trade" happens because sodium or potassium are loosely held by the resin.

Hence calcium an magnesium ions responsible for hardness in the water are removed and replaced by sodium and potassium ions

This process makes water soft.