[@King Tai] Good point, but at least it's an idea for the future.

[@Wick] 
More ideas: 
Manipulate/alter the tree root to be something like a pipe. Have it grow wider and flatter and curl around in a way to seal holes in piping I suppose. Or find the tree the root comes from and use that to seal or slow broken pipes. Possibly use it to clear pipes. I'm not sure exactly what's wrong with the pipes, so I'm just throwing out ideas.

[hr]
Ooooh! I know. If you can alter plants sufficiently, perhaps replacing the pipes with a network of hollow, self-repairing roots and bark might be an interesting way to go about it.

Admittedly, someone with earth/metal related powers would probably do better, but you make do with what you've got.

While we're at it. I want a gigantic elven tree house. The kind where you actually live [b][i]in[/i][/b] the tree.