Disney maintains a very generous policy regarding outside beverages, allowing guests to bring an unlimited amount of water into the parks, provided it is not in glass containers and does not contain alcohol. There is no specific gallon or liter limit, but the containers must fit within your bags or a soft-sided cooler that does not exceed 24" long x 15" wide x 18" high. You are welcome to bring multi-liter bottles or several smaller ones to stay hydrated throughout the day. However, keep in mind that "loose ice" is prohibited at security checkpoints; you should use re-freezable ice packs instead. Most frequent visitors recommend bringing a large reusable bottle, as both Walt Disney World and Disneyland offer numerous filtered water refilling stations and any Quick Service location will provide a free cup of ice water upon request. This flexibility is designed to help families manage costs and stay safe in the intense Florida and California sun, though you should be mindful of the weight you'll be carrying across miles of walking.