Okay, well I just went to refill my boys’ water bottles. I noticed come white stuff on the end of the “spout” and found out the metal of the water bottle is basically… well, I don’t know what to call it. It’s like their little tongues have been wearing away at the metal. I’ll lightly run my nail down the spout, and once i reach that little spot it makes that cringing, nail-against-chalkboard noise.
I swab out (the inside and the outside) the little spout with a Qtip every once in a while, but I’ve never noticed anything. There is that bit of white stuff that makes it almost look like acid caused that little spot
(that caused me to first notice this).
I have the bottles in the dishwasher, but I don’t think I’m going to use them again. I have the boys in a pen right now with just a water crock in there to see if they even know what to do with it. Neither of them have ever used one before, always bottles. I’d rather use a crock than a bottle, as this is actually my second problem with water bottles. The first seemed to just be a bad bottle, but still. 
Any ideas what this could be? They are both acting fine, but I will keep watching them.