Evaporation followed by condensation.
Distillation is the process of heating water to form water vapour, and then cooling water vapour (steam) to get back liquid water. The changing of water into water vapour on heating, is called evaporation (or boiling). And the changing back of hot water vapour (or steam) into liquid water on cooling, is called condensation. Thus distillation involves two processes: evaporation (or boiling) followed by condensation.
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