Using Rain Water???

I decided to catch some rain water in several different locations around my yard this morning and found that the PH is at a dead 6.0 Now do I still have to PH this water or no? I'm considering using it mainly on outdoor plants in between dry spells. They are in 3-5 gals of pro-mix and I have been running the GO line from Gen. Org. Which in itself implies on the box that you don't need to PH adjust. I know the reasoning behind that already just wondering what the deal was with RW and it's PH and buffering capabilities. I didnt want to go dumping this on my indoors as they are used to distilled tap water that is pretty hard :( (150-200 ppm) and i cant help but think the two water types are worlds apart. Anyone who can shed some light on this is much appreciated. And please dont just say get an RO filter lol its on my list im just dead broke and my girl just had our little one a few months ago. Stay green fellas/ladies. Thanks!!