Rain water is fun to collect! From personal experience, though, don’t leave it sitting for too long! I had some that I left for about a week or two, and when I went to use it, it had gone rancid from bacteria in the rain water. It was no good anymore. I’d check it and make sure it doesn’t smell!
Oh heck no lol. I will check it and make sure it is still good to use, I did not even think about that. I may just put it in my hisbicus tree plant and then collect some fresh next time it rains.
Giving it to a plant sounds like the safest option, especially if it’s been sitting for a bit 
hopefully, you can collect some more when it rains again!