Page "The Magic School Bus at the Waterworks" Paragraph 3

Once this occurs, the bus rises up into a cloud along with evaporating water.

Ms. Frizzle makes all the kids get out of the bus by threatening to give them extra homework if they don't.

However, the kids begin shrinking once they're outside and, once they're each the size of a raindrop, they rain down into a river, which carries them into the town's water purification system.

After going through the waterworks, the pipes take the class back to the school.

They come out in the girl's bathroom, where, once out of the faucet, they are instantly restored to their regular size and normal clothing.