If yer correcting someones grammar so you can better understand the point or question they are posing then it's perfectly fine. If your correcting it for any other reason yer just a dork nozzle and come off as a condescending jerk.
Have we gotten so intolerant that we can't even allow poor grammer without being condescending? ...and YES, it is VERY condescending. Teachers are supposed to demonstrate practical life skills as well as Reading, Writing and Arithmitic. I would submit that treating others in a non condescending way is much more valuable in life than proper grammar.
Now, to yer question. The known water damage is VERY likely to be worse than you expected. I would highly recommend a complete investigation. Look in storage areas, under vinyl, under seats, cabinets, beds, etc...
Moisture is our enemy!
Dork Nozzles are not :)