The Magic School Bus - Wet All Over - Ep. 18

The class is excited about going to Waterland. Wanda and Arnold are working on a project together and somehow she convinces him to go to the girls' bathroom with her to get water. He accidentally leaves Ms. Frizzle's keys along with Liz in there, and worse, he forgets to turn the water off. When they leave for Waterland, Ms. Frizzle instead uses a spare key which turns her, the class, and the bus into water. (Note: This episode can be seen as a sketch of the importance of responsibility on the Kids for Character with Tom Selleck.)