Rainwater here for some reason blows my plants up, all plants, all flowers. bushes, trees you name it. With that said I tried it in the hydro system and stored it in a rainbarrel and the result was lots of pest. They sit and lay their larve in the barrels so if you dont get it the first day you are screwed.
When it rains light I put the potted plants from the grow room outside and the next day back in the grow room the dank smell is fantastic.