Your re-usable water bottle can get pretty nasty over time. When it comes time to clean it, try adding a solution of 1 teaspoon bicarb soda and 1/2 teaspoon chlorine bleach to a bowl of water to clean your bottle and its parts.
As ManMade DIY points out, water bottles have become surprisingly complex. While a denture tablet can work wonders for simpler bottles, it's trickier when you're dealing with hydration bladders or water bottles with long tubes (like the one seen above). This solution should help even in hard-to-reach areas. Of course, be sure to thoroughly rinse when you're done, as you don't want any bleach residue leftover in your bottle when you go to use it again.
How To: A Guaranteed Way to Deep Clean Your Water Bottle [ManMade DIY]