Hi Sarah!
Hydration is key when going to Walt Disney World Resort, even in the "cooler" months. Yes! You'll absolutely be able to use your Disney Resort Hotel Refill Mug as an H2O holder. I brought my own refillable bottle in both May and July, and here are my best tips for wetting your whistle during your Disney Days:
~Water fountains can be found near every
restroom entrance.
~Some guests don't enjoy the taste of Florida tap water, so it might be helpful to bring a few flavor enhancing stick packs or liquid drops.
~You'll be able to bring your cup with you as you wait in
attraction queues. Some even have water fountains located within their standby lines!
~Fill up before you leave any
Table-Service meal.
~Bring a few gallon-sized plastic baggies with you to put your (empty) mug in so it can stay clean when in your bag or when safely tucked away in a seat pocket of an attraction.
Due to local food handling laws,
Quick-Service dining locations will have to fill a disposable cup that you can then use to refill your bottle. But, a handful of locations have do-it-yourself soda fountain machines where you can skip the middle step and get a refill of both ice and cold filtered water straight from the machine yourself. These are Backlot Express in Disney's Hollywood Studios, both Restaurantosaurus and Satu'li Canteen in Disney's Animal Kingdom, and both Electric Umbrella as well as Sunshine Seasons in Epcot.
I hope this helped, Sarah, and We'll See You in 2019!
~Kristen