Hello there Arlene, welcome to planDisney, we're so glad you're here!
It is so important to stay hydrated during any Disney trip, especially during the hot summer months! You absolutely can bring in a reusable water bottle with you to the parks, as long as it does not fall under the
list of prohibited items such as glass bottles. We always bring in a water bottle so we can fill it at one of the
water fountains throughout both Disneyland Park or Disney California Adventure Park when needed.
During the really hot days, I usually ask a
quick service dining location for a cup of ice water or even just a cup of ice to add to my reusable water bottle. We also try to remember to take sips of water after each attraction we ride! I've also found that some of the individual hydration packets are helpful to bring to add to your water bottle as well throughout your trip.
I hope this information is helpful for your upcoming trip, Arlene! I'm wishing you and your family a wonderful trip to the "Happiest Place on Earth!"
Have a magical day!
Melissa