What conclusion does Phoebe draw about the latest note about water in a well in Walk Two Moons?

Phoebe thinks the note might mean that her mother is hidden in a well.
Phoebe doesn't know where her mother is. She believes that the messages she's getting are a sign that the lunatic kidnapped her. The lunatic is a man who showed up at Phoebe's house looking for her mother.
One of the notes says, "We never know the worth of water until the well is dry." Phoebe believes that her mother might be in a well. She's very upset that the police don't seem to be taking the notes or her mother's disappearance seriously. She believes that the lunatic might be leaving the notes.
Ultimately, her mother returns home. Phoebe finds out that the lunatic is actually the boy that her mother gave up for adoption long ago. She left to try to have a relationship with him. The notes were from Mrs. Partridge, and they were meant to be encouraging and kind.