I once received PLA that was "moisturized" from a Chinese supplier. Sending back from Europe to China was way to expensive, so I did put the PLA in an oven at 60°C for about 20 minutes. After that, it printed perfectly :-)
I keep my opened reels inside sealed plastic containers, with moisture catching bags inside ...
Depending on the outside weather, leaving a reel of PLA "unprotected" (sitting on my desk), for about 2 weeks, is enough to see the print-quality degrading ! (I use RRW PLA, bought from 123inkt.nl)