Some plumbing franchises (Rotorooter, for example) have gotten in to water damage restoration, but smaller, independent guys would probably like to team up with you.
With most of them, it isn't about any commissions you might pay, but them being able to be of better service to their customers, and for them to be able to focus on what they do best.
A pretty smart salesman once told me:
"People pay to make problems go away"
Help these people see that you can help their customers, and help them have one less annoyance, and its a good start.