Coco Key is both a water park and hotel but they do offer day passes to just the water park and there are often deals on Living Social or Groupon so be sure to check ahead of your visit.
There are 3 taller slides you can see off the side of I-4 and then the splash area with more slides pictured above. Oh yeah, and that big bucket up top... see it... it dumps all over the place every so often. Super fun!
Step inside the covered area and there is a nice pool with a few more slides where you can escape the sun and cool down. They also have a poolside bar along with an arcade and cafe. Check it out and see for yourself!