Yes, you are absolutely allowed to bring your own water into the Disney theme parks, including Walt Disney World and Disneyland. Disney’s official policy permits guests to bring outside food and non-alcoholic beverages for self-consumption, provided they are not in glass containers and do not require heating or refrigeration. You can bring factory-sealed plastic bottles or reusable metal and plastic water bottles. This is a highly recommended strategy for staying hydrated while saving money, as bottled water inside the parks can be expensive. Just remember that if you bring a cooler, it must be within the size limit (24" long x 15" wide x 18" high) and cannot contain loose ice; reusable ice packs are the approved way to keep your drinks cold. There are also numerous water bottle refilling stations located throughout the parks, particularly in newer lands like Galaxy's Edge, making it easy to top up your personal supply throughout the day.