There was a thread a couple weeks ago about rainwater. The general consensus was don't use it. The advice given at that time from a few of the senior people on this site, was to wait until you save up enough for the RO
. Distilled is pretty cheap at Walmart, and other stores. I feel you on the money issue. Unfortunately this hobby gets expensive quick, but there are ways to scrape by if your on a budget. You just have to be creative and patient. Good luck getting everything setup, its always exciting building a new tank.