Just try to answer the question yourself, if phrased a different way. If WDW, a place the size of the city of San Francisco, with 4 theme parks, 2 water parks, and 23 resorts, has provided its guests with water that will make them or their dog sick, wouldn't we have heard about that by now?
MK opened in 1971, Epcot in 1982, DHS in 1989 and AK in 1998. Annual visitors to WDW in 2007 were estimated to be:
__Magic Kingdom, 17 million visits (No. 1 worldwide)
__Epcot, 10.9 million visits (No. 6 worldwide)
__Disney's Hollywood Studios, 9.51 million visits (No. 7 worldwide)
__Disney's Animal Kingdom, 9.49 million visits (No. 8 worldwide)
http://en.wikipedia.org/wiki/Walt_Disney_World_Resort