If stored rainwater has been kept in a sealed container (even milk jugs will do), and not exposed to light (esp. sunlight*), the gases and minerals are not going anywhere, and bacterial growth should be minimal. Basically, if the rainwater water looks clean and clear, it should be fine for plants.
Note however that uncapping a container a couple days before using it will “aerate it” quite well if the water level is where the container reaches full diameter or width. (This is a small consideration for me with our well water, which is NOT very aerated, of course. But, then again, chicken guano compost has LOTS of nitrogen in it, and we, er, our chickens, generate plenty.)
*A milk jug of rainwater exposed to sunlight will of course go “green” quickly. In a shaded indoor environment (covered / no direct light), it should keep for months. This assumes reasonably clean roofing and guttering as the “collector”. In my case, the rainwater presently comes right off a large awning. To save more water, by happenstance to this discussion, I in fact just bought a 55 gallon plastic drum @ Rural King today, using some rewards $$. It was on sale ($19.60). I’ll have to make sure it’s not translucent - if so, I’ll paint the exterior black or dark blue with some spare paint. (Opaque containers are best if light can get to the container.)
Thx. I would add smell.
, I in fact just bought a 55 gallon plastic drum @ Rural King today, using some rewards $$. It was on sale ($19.60)
Good price. I use washed, old trash bins, preferably with lids. I cover some others with screening to deter mosquitoes. Spraying non-stick food spray helps also.
Good info. I save gallon milk jugs and fill them from my rain barrel, then put them in the greenhouse in the back section, under a shelf that gets little sun. I have had a few ‘go green’ through the years, so those just get dumped. I have about a dozen on hand at any time, though I don’t store them over winter - they freeze and thaw and leak and just make a mess.
Otherwise, I use that water in the spring when I’m starting seedlings, and then all season long when I have pots of things to water daily, and in the fall when I’ve got salad greens growing in there. It saves me from dragging out the hose for that task, plus it’s that magical rain water! :)