Why not use rain water? Depends. Here in Colorado it has been deemed by the courts to be illegal unless you own water rights with your property, and very, very few homeowners, if any, do. We did use rain water a while until we found out how bad the fine can be. It does require cistern storage, which requires input filtration, monitoring for bacteria, etc. It is great, I agree, and quite worth going thru the process of setting it all up. We even switched to an all-steel roof to help. Some health dep'ts require regular testing and certification of rain water that is used for domestic consumption. Here in my rural area, that isn't a requirement for any of our water [and, of course, we aren't supposed to use rain water....] We have a friend who was fined in Denver for having a roof-gutter downspout running into a barrel, from which he drew water for his garden.
However, we put in a well a while ago and the water is hard. Full of sodium, for one thing. So, after having that nice rain water, I put in a reverse osmosis system for drinking and cooking [haven't decided what to do about the general house water for other uses....]
I went with a Blue Air unit. These are more expensive than some of the others, at $3000. Some of the less expensive ones have numerous filters that must be regularly changed, and these can really be pricey. An inline cartridge filter for any sediment or fine particles, installed somewhere prior to the rev. osm. unit, will keep the particles out and save the rev. osm. membrane. That also negates the need for fancy, multi-stage filters at the unit, which some are sold with. Our replacement cartridges are around $4 each, and I go through a couple a year, though our well water is really clean.
Some osmosis systems also have a replaceable carbon filter unit. From what I understand from shopping for this stuff last summer, these filters are on the output side and are to further condition the water which has been sitting in the rev. osmosis unit since the last time you turned it on. The unit we bought doesn't hold any water, so that's not needed. Another saving.
According to the info' we got with our unit, there should be no bacteria coming from the output of the unit. The pores in the membrane should stop them. [I don't know, though, I haven't had ours tested but in our case the bacteria would have to originate in the well water and it's been tested negative for that.] That would mean, I would think, no uv purification is needed, in answer to that question. I suppose that if your source water is contaminated, you might have to something on the source water side. I have read somewhere that too much bacteria being filtered out by the rev. osm. membrane can leave that membrane less efficient due to the bacteria blocking some pores. However, supposedly the periodic flushing of the membrane the units do should clean that off. But I don't know and you'll have to mull that one over.....
