The Magic School Bus at the Waterworks - Joanna Cole, Bruce Degen
The Magic School Bus is just really a solid elementary science series. It's informative, but not dry. It's funny, but not overly corny. The illustrations are attractive, but not too cutesy. In short, a really nice series. This one covers the water cycle as well as water purification. Not the most dazzling scientific subjects to be sure, but important nonetheless and handled quite well here. I also love the section in the back for serious students.