It shouldn't matter on the distiller whether you use Aluminium or stainless steel, as your interest is in the steam that boils off, and I doubt fluoride and Aluminium can become volatile and boil over. They are salts which are left behind when the water evaporates. They will build up and cause residues which will interfere with heating evenly, and should be removed periodically. But they don't boil over with water.

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