Keep tenant security deposit or return it?

[Collin Perry]

I have tenants that recently gave notice to vacate. They moved all their stuff out a couple days ago and we’re gone from the apartment for 3 days. They came back this evening to clean and there was water all over the apartment floor and leaking from the hot water heater in one of the closets.

I believe a flex pipe fitting came lose or was damaged due to the tenants moving their personal items out but that’s hearsay. I can’t 100% confirm that.

Located in WA State. How should I proceed with their security deposit?