You can only purchase up to a 10 day ticket. That is considered the "break even point" for purchasing an annual pass. I would do the math though, with the last annual pass increase.
You could add the Park Hopper plus option to a 10 day ticket. That would give you 10 visits to the water parks, mini golf and your 10 days to the themeparks, with the flexibility of going to one park in the am and another (Epcot) for dinner.