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

(N/A) Demineralised water is free from all soluble mineral salts. It does not contain any anions or cations.
Demineralised water is obtained by passing water successively through a cation exchange (in the $H^+$ form) and an anion exchange (in the $OH^-$ form) resin.
During the cation exchange process,$H^+$ exchanges for $Na^+, Mg^{2+}, Ca^{2+},$ and other cations present in water.
$2RH_{(s)} + M^{2+}_{(aq)} \leftrightarrow MR_{2(s)} + 2H^+_{(aq)} \dots (1)$
In the anion exchange process,$OH^-$ exchanges for anions such as $CO_3^{2-}, SO_4^{2-}, Cl^-, HCO_3^-$ etc. present in water.
$RNH_{2(s)} + H_2O_{(l)} \leftrightarrow RNH_3^+OH^-_{(s)}$
$RNH_3^+OH^-_{(s)} + X^-_{(aq)} \leftrightarrow RNH_3^+X^-_{(s)} + OH^-_{(aq)} \dots (2)$
$OH^-$ ions liberated in reaction $(2)$ neutralize $H^+$ ions liberated in reaction $(1)$,thereby forming water.
$H^+_{(aq)} + OH^-_{(aq)} \longrightarrow H_2O_{(l)}$