Kaitlyn,
Thanks for asking your question to planDisney!
I was just at
Disney's Typhoon Lagoon Water Park a few weeks ago, and it was looking fantastic! You will have so much fun there!
The Theme Park Reservation program using the
Disney Park Pass System is, as you suggest, just for the four theme parks. You do not have to make a park reservation for a water park.
BONUS TIPIf you would like to plus up one of your water park visits, I strongly recommend you consider booking either a
Beachcomber Shack or make a
Typhoon Lagoon Umbrellas reservation. In both cases you get a "home base" where you can keep your belongings and give your family a place to meet up. In the case of the Beachcomber shacks, you also get a nice, secluded place with incredible views of the wave pool for your family to connect and relax between activities. Just call (407) WDW-PLAY or (407) 939-7529 to make a reservation.
Write me back if you have any follow-up questions.
Have a Magical Vacation!Doug