User blog comment:FairyRaven/Fairy Tail Chapter 428: When We Take Different Paths, Review and Commentary/@comment-76.121.234.236-20150415065247/@comment-7418318-20150416205541

I think it's not BS. If you stay out in the cold rain you will get sick not because of the water, but because your body get's too cold.

I see no reason why being a water mage would make Juvia immune to cold temperature and where it rains it usually is quite a bit colder than when it's dry.