During the summer months, I completely understand bans on rainwater remaining stagnant in our area. We live by the river, so mosquitoes can get really bad; stagnant water only encourages their breeding, so it makes sense that the city wants to discourage people from leaving water around.
That said, if you want to collect water in your own containers to be used over again, there’s nothing wrong with that—and the city doesn’t penalize you. The entire state of Oregon, however, is not like my town. They are penalizing a man with a month in jail for collecting rainwater on his own land.