My aluminum water bottle smells gross!!!?

Sad to say, if your bottle was made poorly or has any form of cracks in it (no matter how small) it could have mold that has grown in it. Sorry to gross you out. I've had a few coffee mugs where the outside linings have cracked and the same thin happened. If in doubt, try washing it out with some vinegar and baking soda (let it fizz up) and then rinse with hot water. Don't use it for a while. Let it dry out completely and see if there's any difference.