Hi Kevin!
Welcome to the Disney Parks Moms Panel, and thank you so much for bringing this question to us hEAR!
Staying hydrated is important as you have fun in the Southern California sun, and so I'm very happy to say that no, guests are
not restricted to any size limitations of water bottles brought in to Disneyland Resort. I've seen guests walk around with the gallon plastic bottles that are purchased directly from a store shelf, and I've seen guests with double-wall stainless steel insulated monster sippers. Both (and everything else in between!) are perfectly fine,
as long as your container is made of any material other than glass.
Do note that personal property rides with its owner on all Disney attractions, and while most of the more thrilling rides do have seat-back pockets, a gallon might be too wide for these. And since a lot of attractions unload in a different area than where they loaded, there isn't an option to leave your stuff behind and get it afterward, so I will say that you might benefit from having a backpack or
renting a locker to store such a large sized container.
As far as refilling your container, definitely take advantage of water glasses and refill pitchers at any
Table-Service Disney Dining Location that you already have reserved. Look for
drinking fountains near all
Restrooms, and additionally taller filtered water bottle refilling stations are starting to pop-up all over; there's one near the exit of Autopia, and there are a few on the planet of Batuu in Star Wars: Galaxy's Edge.
You can also request complimentary cups of ice water at any
Quick-Service dining location, though these are usually the smallest size. However, and here's a pro tip: some of these locations have self-service beverage machines, so when you request a complimentary water cup, you can use that to refill your bottle completely. These locations are Alien Pizza Planet and Boardwalk Pizza & Pasta. GCH Craftsman Grill has a self-serve machine, but this location is inside Disney's Grand Californian Hotel & Spa, so you would need to re-clear security. The Plaza Inn has a self beverage area, but is only accessible during lunch and dinner times. Rancho Del Zocalo Restaurante has self-service machine inside their ordering area, but they also have a filtered water spigot outside near their plastic-ware and condiment area. And my favorite is a Coca-Cola snack stand directly across from Soarin' in Disney's California Adventure Park. Again, you'll have to ask for a water cup, but you'll be able to fill up fully with ice and water over here.
And speaking of Soarin', did you see that
Soarin' Over California is BACK for a limited time?? This classic version is making a special appearance with the
2020 Disney California Adventure Food & Wine Festival, both happening daily now through April 21.
I hope this helps you stay hydrated, Kevin, and We'll See You Real Soon!
~Kristen