What is the best method to recycle waste water?

Question

Cost and enviroment

Answer 1

The cars powered by hydrogen fuel cells that the Bush Administration has partnered with the Detroit Big Three automakers to develop could eventually be pulling up to wastewater treatment plants for fill-ups, say Penn State environmental engineers.

industrial wastewater, for example -- and simultaneously clean the wastewater.

Answer 2

I think it depends on what scale you are looking to purify the water.  

If you are looking at a small scale, like for your house or some such, I think a solar still is the most economical.  It is kind of like a greenhouse that evaporates the water from the waste water, and lets it run down a slanted roof into a trough.  What you get is a source of fresh water, and some left-over sludge which you flush out once a day.  You can check out the details at http://www.i4at.org/surv/sstill.htm and other websites.