Deionization is the process which removes the negative ions from water, thus decreasing its conductivity. This is very beneficial in the laboratory/industrial sector.

In distillation, water is heated in a chamber and turned into vapor (steam). This water vapor rises leaving impurities behind in the boiling chamber. The purified vapor then enters a condenser where it is cooled and returned to the liquid state.

More distillation [local].

A comparison [local] of water treatment technologies.