This 'environmentally friendly' angle is a load of rubbish, unless you're using it as a selling point. From the point of view of the Earth, the Earth will be fine regardless of what we do to it; hell; the whole meaning of life could be that the Earth created all us human beings to make plastic because it wants to ingest plastic bags, and once it's had its fill, will wipe us out.
It's us that's in trouble, not the environment, so whether it's ladders or WFP, both are the same with regards the environment; I really don't think the Earth is bothered whether we use ladders or pure water cleaning systems.
But as an environmentally friendly selling point, rain water harvesting is the most 'environmentally friendly' way of creating your pure water.
Now I hope this isn't a clever way or gerrymandering a post in an underhand manner of advertising a certain companies product. We've seen this done many times before, and it always leads to tears.
