You should be able to get the mold out of the water bottle by washing it out with a little bleach and using a baby bottle brush.
Plug the kitchen sink up and then pour a little bleach into the sink, then fill the sink with water and then soak the water bottle in the bleach and water for about 10 to 20 minutes.
Then take the baby bottle brush and scrub the mold out. The bleach will help kill the mold.
Just be sure to really rinse out the water bottle good to get rid of the bleach.