cost of tenant negligence

[Ana Vhan]

Tenant in my Washington state rental moved out and we find out an active leak underneath the kitchen sink. It looks like its been leaking for some time now as it has damaged the cabinet underneath. The tenant mentioned that he did notice some pipes coming down from garbage disposal. He should have notified us the first time he noticed this but he did not. 

Also, the water heater tank is leaking in the garage which we noticed at the time of final walkthrough. Again he failed to report it when it first happened. 

How would I handle such situation? How much can I charge him for this negligence? Of course, I need to charge him for the damages but we had a similar leak last year that caused us tearing down entire kitchen and installing a new one. I am terrified thinking of the potential damage/mold in the wall behind the sink cabinet. 

Thank you. Appreciate your inputs.