According to Merriam-Webster, an arsonist is a person that engages in "the willful or malicious burning of property (as a building) especially with criminal or fraudulent intent".
Flooding can also cause serious damage to buildings or other property. Although it is probably significantly less common, I could imagine that a person might maliciously flood property with criminal or fraudulent intent.
For example, if the residents are vacationing away from home, it would be easy enough for a person to cause serious water damage to a house by turning on all water spouts and plugging all drains. This occurs in the movie Home Alone:
Harry: [Marv brings a load of stolen goods from the Murphy household to the van and Harry sees him laughing] What's so funny? What are you laughing at? You did it again didn't you? You left the water running. What's wrong with you? Why do you do that? I told you not to do it.
Marv: Harry, it's our calling card!
Harry: Calling card.
Marv: All the great ones leave their mark. We're the wet bandits!
Is there a word for such a person? In other words, arsonist is to fire as what is to water / flood?