When Lighting strikes across the skies, it puts a natural nitrogen into the rainwater,... plus good shit that we don't even know about. Even if it just a little sprinkle, that rain water will do awesome good things for your plants. However, after a down pour, give the Plant's enough time to absorb the rainwater until they are completely hydrated, then shake off the excess, like a nice breeze would do. Save as much rainwater as possible, & soil/foliar feed with it. Cover one week prior to harvest when rain is coming. Hope this helped.