Yeah, I am pretty sure the only rules were about collecting or redirecting runoff, not simply letting the rain water plants directly. Of course if you are doing major construction, moving earth, digging ditches, pouring concrete, or similar, you are going to have to get a building permit and environmental impact will be a part of that.
I definitely wouldn’t recommend drinking from a rain barrel, nor would I shower with it. I am sure it is possible to operate one in a safe fashion, but I wouldn’t really count on most people doing it properly.
