Green everything? What?
Being a bit more reasonable in my expectations.... (And totally reserved concerning our impact on the environment...) I will try to limit my response to How do I live "green" in my hobby....
While I would love an R.O. unit for convenience sake, I am not sure from the "Green" standpoint that it qualifies by itself, (who is recycling old filters and broken units?) although as pointed out, it is sometimes better than some alternatives. Being "green" is to measured by degrees, and is not a black and white viewpoint. So as I say, I am glad that someone found a better way of doing something.
So what do I do that could be considered some degree of "green"....?
I collect enough rain water from one gutter to fill all my CP needs, with a little left over at times for my other plant hobbies and needs (I don't collect enough for everything at all times, but could if I didn't mind making my entire yard/house look like a hodge-podge farm of sorts). (I'm Married!)
Rain water is collected off a gutter using a couple of recycled 55 gal. barrels (To be safe, make sure you use barrels that were from non-toxic/food grade products. There are some that are produced for toxic/caustic chemical use, and reuse can be risky). I also reuse old kitty litter bins and containers to store the water in my greenhouse over the winter, which sits in a sunny position to help create residual thermal mass to hold the days heat, and release it during the night. (Something I picked up from Mother Earth News about 40 years ago.)
I use the natural sunlight for way over half my plants (in a greenhouse and growing outdoors), and supplement my indoor lighting needs with sunlight, by having the plants I have under lights, in front of windows. By receiving sunlight for part of the day, I am able to have the lights on for less time.
I reuse all the old potting medium, dead plants and other used components, to plant up other new plants, Non-CP plants... or whatever won't be of use there, the remains goes into the garden or compost heap for conversion. (Anything diseased does not.)
As an old long time advocate of organic gardening (thanks to an amazing, down to earth Uncle) long before it became a "trend", making the most of things and reusing everything you could was the logical thing to do. (Anyone here remember Mother Earth News?)
A few guys I know laugh when we see some "new "Green" way" of doing something, as it is usually something we had been doing all along! Seems if you are around here long enough, you will find that people like to "re-discover" things and call them new! (Usually for prestige or money!)
Well, that is about all I can think of for the moment. I would love to say I am doing something admirable and complex, and costly, like having an expensive windmill generator or an array of solar panels on my roof to supply all my electrical needs. That really makes others envy you, when you have lots of cash to blow in the name of some worthy cause.
But to be honest, it is people with little or no money who come up with the good "green" ideas. Like the college kids here, who can't afford the water or electricity, and so find ways to be "green" without spending "green"! These are the people I admire! Besides, what do you do with a solar panel when it is busted and the sun has cooked the crap out of it and the parts are brittle and of no use? I wonder!
Oh, if you are interested in people who lived their entire lives nearly as "Green" as possible, get yourself 60 or 70 years worth of old National Geographic magazines, and just look at the pictures. In the oldest ones you will see small societies of people who once lived "green", with very low, negative impact on the natural world.
"Modern, civilized society" however used to look down on those people and call them "savages"! Ironic!
I am not sure if any of this is what you are asking for, but this is all I got.
Oh, coir! Yes, use it, like it. Haven't been using it for long enough to know the long term results however. And yes, it doesn't absorb waster like peat does. It holds it by its structure, but in a different way than peat. Nothing a little extra watering won't solve.