We're going to WDW for a 3-day weekend of MNSSHP, waterparks and resort time in late August. Since we plan to visit both waterparks during our trip, I was considering buying water park annual passes, in case we want to do a similar waterparks weekend at WDW next summer. I did this once a few years ago and seem to recall that water park annual passes are activated upon date of purchase rather than upon date of first use. Is that correct? If so, then obviously I should wait until our first water park day to buy the passes, so I thought I'd verify. Couldn't find this info on the Disney website.