If your making it and adding something with it that has to be filtered after being added to the bac. water, then there's no need to filter it before adding it. As it will just be filtered in the end, giving the same result anyways. If your making something that's going to be filtered first, then you add your bac. water afterwards and don't filter after adding, then it's probably a good idea to filter your bac. water first. Hope this clears it up for you.