I was using rainwater for my discus, rams, and to breed my tetras. I did collect it from my gutters, but I had previously tested it and it was fine. However I noticed a lot of my fry and some of my rams dying so I again tested the rainwater and it was sky high in nitrites. I would definitely suggest testing it before using it to avoid this kind of problem. Before the nitrite problem though, the ph was perfect for the discus, rams, and breeding and they seemed to do well in it. If it isn't going through any gutters, etc. it is probably fine but I would still test it to make absolutely sure.