What is meant by 'demineralised' water and how can it be obtained?

(N/A) Demineralised water is water that is free from all soluble mineral salts,such as those containing $Ca^{2+}$,$Mg^{2+}$,$Na^{+}$,$Cl^{-}$,$SO_{4}^{2-}$,and $HCO_{3}^{-}$ ions.
It is obtained by passing water successively through a cation exchange resin (in the $H^{+}$ form) and an anion exchange resin (in the $OH^{-}$ form).
$1.$ In the cation exchange process,$H^{+}$ ions are exchanged for $Na^{+}$,$Ca^{2+}$,$Mg^{2+}$,and other cations present in the water:
$2RH_{(s)} + M^{2+}_{(aq)} \longrightarrow MR_{2(s)} + 2H^{+}_{(aq)}$
$2.$ In the anion exchange process,$OH^{-}$ ions are exchanged for anions like $Cl^{-}$,$HCO_{3}^{-}$,and $SO_{4}^{2-}$:
$R'NH_{2(s)} + H_{2}O_{(l)} \longrightarrow R'NH_{3}^{+}OH^{-}_{(s)}$
$R'NH_{3}^{+}OH^{-}_{(s)} + X^{-}_{(aq)} \longrightarrow R'NH_{3}^{+}X^{-}_{(s)} + OH^{-}_{(aq)}$
Finally,the $H^{+}$ and $OH^{-}$ ions released in the process combine to produce water:
$H^{+}_{(aq)} + OH^{-}_{(aq)} \longrightarrow H_{2}O_{(l)}$