I was never a big "Friends" fan. I did like his work on "The West Wing." he showed he could play serious characters.
this is just speculation, but I read that he had been playing Pickleball for 2 hours before he came home and got into the jacuzzi. If he had a heart attack or some other type of medical incident, he could have lost consciousness and that could have led to his drowning.
I hope it wasn't a drug or alcohol relapse, but with his history, people are going to look at that possibility.