Hi Skye!
I'd love to tell you the Give a Day, Get a Disney Day vouchers are good for water park use, but unfortunately, they are
not. The vouchers from Give a Day, Get a Disney Day are valid for use at one of the four main theme parks: Magic Kingdom, Animal Kingdom, Hollywood Studios, or Epcot. I've included a link to read through the
terms and conditions.
As for Blizzard Beach and Typhoon Lagoon admission, if you plan on visiting the parks with a Magic Your Way multi day ticket, you can currently add the Water Parks and More Fun options for 50% off (about $25/ticket). Another option is to look into the FL resident Water Parks after 2pm Annual pass, which costs about $20 more than a one day water park ticket. Not exactly as great a deal as the free admission you'll get with the GADGADD voucher to the main parks, but hopefully you'll be able to use this info to celebrate summer at Walt Disney World!