Yes, you are absolutely allowed to bring a metal water bottle (such as a Hydro Flask or Yeti) into Disneyland and Disney California Adventure. Disney's official policy permits outside food and non-alcoholic beverages for self-consumption, provided they are not in glass containers. Metal canteens are actually encouraged as a sustainable and cost-effective way to stay hydrated in the California heat. There are numerous "Refillable Water Stations" and traditional water fountains located throughout the parks, particularly near restrooms and in newer areas like Star Wars: Galaxy’s Edge. When you pass through security, you may be asked to open the bottle if it contains liquid, or simply show that it is not glass. Keeping your metal bottle filled with ice before you enter the park is a popular "pro-tip," as the double-wall insulation will keep your water cold for most of the day, saving you from paying the high prices for bottled water inside.