Hi there, Danielle, and welcome to planDisney. As a fellow U.K. resident, I've been lucky enough to buy the Magic Ticket myself. It's a really magical offering, and I know you will appreciate the Disney
Water Parks access in the steamy heat of August!
On to your great question... at this time, you do not need a
Park Reservation to enter the Water Parks. This means that if both
Disney’s Blizzard Beach Water Park and
Disney’s Typhoon Lagoon Water Park are open, you could visit both in one day without making a reservation. Coincidentally, I was just talking with friends about Disney’s Typhoon Lagoon's WILD wave pool. I guarantee you will never have experienced a Water Park wave like this before. Top tip - don't bring in sunglasses!
If you would like to visit a Water Park in the morning and then head to
EPCOT that evening, I would make a Park Reservation for EPCOT for that day. Even if we think we are likely to have a Disney Resort hotel day or a Water Park day, we usually go ahead and make a Park Reservation for each day of our ticket as you never know if you may like to pop in to see some evening entertainment. Once your Park Reservation is in place, you don't have to worry about the administration side of booking it while on holiday.
Another job I recommend ahead of your trip is to download the
My Disney Experience App. It's a great help in the Parks, providing access to up-to-date ride wait times, Mobile Food and Beverage orders, and much more - worth checking out before arrival.
Danielle, I hope you have the most enchanted time at Walt Disney World. Please let me know if I can help with anything else for your adventure. Enjoy the magic! Louise.