Oh man, that's rough. Exactly how did the electrician manage to "accidently" open a water valve? Was he installing an electric water heater and hoping to fill it up so it wouldn't be fired up dry?
I once lit off an RTU that I had installed a new heat exchanger into. Forgot about the protective oil coating on the exchanger. Smoked up the real estate office pretty good. I kept wondering what all that yelling was about down below!
Hindsight being 20/20, next time wire the water cutoff valve shut and slap a tag on it. Though instances like this are commonly referred to as Murphy's Law, my father-in-law prefers his label of the "Law of Contrariness". Just when you think nobody on God's green earth will touch that valve while you're out of range, somebody will!
Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.