Hello Dominic,
Thanks for visiting planDisney with your question. There is so much to see and do at Walt Disney World, adding the
Park Hopper Plus Option gives you the flexibility to experience all 4 theme parks, both water parks, miniature golf, and so much more!
At this time, you do not need to make a reservation to visit
Disney's Typhoon Lagoon, but you will need either the Park Hopper Plus added to your tickets, or you'll need to
purchase a separate ticket for the water park. Whatever you choose, you'll still
need to have a reservation to Magic Kingdom if you plan on visiting it later in the day because you technically won't be park hopping. Park hopping is only among the 4 theme parks:
Magic Kingdom,
EPCOT,
Disney's Animal Kingdom, and
Disney's Hollywood Studios. You also won't have to wait until 2:00 PM to visit Magic Kingdom for this reason. As soon as you are done enjoying Typhoon Lagoon, you'll be able to head to a park for the day, but you will need a reservation to whatever theme park you want to go to.
You could also decide to start your day in Magic Kingdom, head to Typhoon Lagoon to cool off in the afternoon, and then go to EPCOT or another park in the evening. If this were the case, you would only need to make a reservation to Magic Kingdom. After that you could return to Magic Kingdom or head to EPCOT without another reservation.
Hope this helps. Have a magical vacation!
Diane