Are you sure it was a water tower? Warriors of Virtue (1997) From IMDB: Ryan Jeffers (Mario Yedidia), a disabled youth, dreams of joining the school's football team. During an initiation rite, he is swept away through a whirlpool to the Land of Tao. There he is hunted by the evil Lord Komodo (Angus Macfadyen), who needs the boy as a key to enter the other world. Ryan is rescued by the protectors of Tao, five humanoid kangaroos embued with the five elements and virtues. Here's the movie trailer: http://www.youtube.com/watch?v=LzofuNqUb4c
Right now, I can't think of a film that combines a water tower and a magical land. "The Odyssey" is a TV series in which a boy lapses into a coma after a fall and has adventures in a fantasy world in which the age limit is 16 (as I recall).