So the plumber interviewed noted that the pipes 'unthawed'. If that were the case they'd still be frozen
Thawed is a real word and while unthawed might potentially qualify, if it were one it would mean 'froze'.
As for it happening to so many public schools I would attribute that to their management. Some clueless enviro-clown in upper management probably calculated how many tons less carbon would be emitted if they set the building temperatures down to 6 degrees C while they were unoccupied. They forgot to calculate how many hydrocarbons would be combusted by the numerous repair vehicles and the carbon embedded in the materials required for all of the repairs
Send them to the Gulag!
I'll give you one guess as to how the responsible individidual(s) voted in the last election. My money bets that they're party to more than one disaster.