Boiling removes only temporary hardness of water.

During boiling, the soluble Mg(HCO₃)₂ is converted into insoluble magnesium hydroxide and Ca(HCO₃)₂ is changed to insoluble calcium carbonate..

In permutit process hydrated sodium aluminium silicate is zeolite/permutit. For the sake of simplicity, sodium aluminium silicate (NaAlSiO4) can be written as NaZ. When this is added in hard water, exchange reactions take place

$2{\mathrm{NaZ}}_{\left(\mathrm{s}\right)} {{\mathrm{M}}^{+2}}_{\left( \mathrm{aq}\right)}\to \mathrm{MZ} \left(\mathrm{s}\right) +2{\mathrm{Na}}^{+2}{ }_{\left(\mathrm{aq}\right)} (\mathrm{M} =\mathrm{Mg}, \mathrm{Ca})$

In permutit process only cations causing hardness are removed.

In Ion-exchange process both the cations and anions causing permanent  hardness of water can be removed, for this process cation and anion exchange resins will be used.De mineralized water will obtained after the process.

Hence, the best method for removal of hardness of water is ion-exchange process