Hi Karen and welcome to planDisney!
How exciting that you will be arriving at
Walt Disney World TODAY - I am not jealous at all!
You absolutely can bring your own bottles of water into the theme parks and water parks with you.
My family always do this when we visit in an attempt to stick to our budget (without having to go without other essentials like a new pair of mouse ears for my collection).
The official policy states that "Guests are allowed to bring outside food and nonalcoholic beverage items into the park for self-consumption, provided they are not in glass containers and do not require heating, reheating, processing, refrigeration or temperature control and do not have pungent odors."
I'm not sure how you plan on storing your water bottles but, it might also be worth noting the following
park rules:-
1/ Suitcases, bags, coolers or backpacks, with or without wheels, larger than 24" long x 15" wide x 18" high (61 cm x 38 cm x 46 cm) are not allowed in any theme park or water park.
2/ Loose or dry ice is not permitted in these containers. Re-usable ice packs are recommended.
Karen, did you know that there are also multiple places to replenish your water bottles throughout the Walt Disney World Resort? Take a look at this handy list of
Water Bottle Refill Stations.
You will also find that iced water is available for free at most
Quick-Service dining locations.
I hope that this has answered your question, Karen, and that you have the most amazing visit to Walt Disney World!
Emma