Hi Emily,
Thanks for stopping by to see us here at the Disney Parks Moms Panel with your question!
I'm so glad to see you have plans to stay well-hydrated in the Florida sun and heat this summer. In all parks, you may visit any quick service dining location and receive a cup of ice water upon demand. You are also welcome to bring a water bottle and fill it at any of the water fountains located throughout the parks.
I do understand that there are bottle-filling water fountains popping up in various locations; one I am sure of is located in
Cosmic Ray's Starlight Cafe in Tomorrowland in the
Magic Kingdom Park. You can always stop a friendly Cast Member and ask where the best place to fill a water bottle would be and they will be happy to help out.
I find myself feeling thirsty when I finally stop moving, which usually means when I am waiting in line for an attraction, so I keep a bottle of water on me to hydrate while I wait.
Emily, I hope you're well-hydrated and have a fantastic visit! Come see us again with any additional vacation planning questions.
Best Wishes,
Amy S.