Rain and tap water question.

[Ross]

Rain water in most areas is pretty soft (lacking nutrients (except, perhaps Nitrogen if a thunderstorm is present). Tap water could be anyone's guess. If well water, you can can only guess unless you have an analysis done (not cheap) but most municipalities will tell you the analysis of the city water. Mixing is fine. As for how to blend fertilizer, that gets more complex and I just avoid the issue by using straight RO water.