For this particular instance, I think I have a decent suggestion.
Given that dome of stars ceiling is collapsed, it's entirely reasonable that all the cauldrons gathered a layer or 2 of water from rain. Cauldrons with water, lava, & presumably powdered snow (though I haven't found opportunity to test this) can't be used as restock because they are different blocks from the base cauldron as far as the game is concerned (`water_cauldron`, `lava_cauldron`, & `powdered_snow_cauldron` respectively, compared to `cauldron`).
In fact, the version of v3osgil on EQ seems to have implemented exactly that solution.
For better color matching, I suppose you could set cauldron block to be swamp or pale garden biome (or even use a custom biome with custom water color), but like I said earlier, it's fairly reasonable that these particular cauldrons would have water in them given how open to the sky they are.