I would consider all fresh water unsafe, just to be on the safe side. Of course 5 minutes of a rolling boil will take care of that.
Depends on where you go to swim, it is a place with some rapids, it might be fairly safe for swimming....
I would not trust wells too much....
Deet does indeed keep the little ones from biting, most of the time...so does Citronela or Deporte...and cheaper, too.
Always sleep with a mosquito net...shake out shoes before putting them on...be careful around piles of dirty clothes (for some reason centipedes love this stuff.)
HB