Using ray of frost to free water is something that in dnd would in most cases be left up to dm interpretation in heavier rp games most dms would let something like that apply just most players for games do not think outside the box. The idea behind the game was to make it similar to dnd where thinking outside the box is encouraged. Thus several mechanics. Not just ray of frost where this could be used.
That should really be the Shape Water cantrip for freezing water. Create Bonfire for creating a patch of fire. If they would just use the rules as written, they could have their surface effects. The attack cantrips are really just that, attacks, Pretty much so that Wizards don't need to carry around crossbows.
