Existing greywater or sewage to potable systems
In the references file you will see some stuff about municipal water recycling systems. There are also a few patents on home water treatment systems to go in your basement. I remember just hearing vague whispers about a basement system that was on the market there for a while back in the 60s (before they had laws against recycling water back to potable, I guess,) too, called the cyclet, cycle-let, or the cyclelet.
There are 2 examples I could find of cities practicing direct potable reuse:
Cloudcroft, new mexico
and there is the Denver water recycling demonstration plant (it seems unclear whether that water is actually going back into the city supply system, though). These systems always need a good deal of new water input, because people in the city will remove water from the system by using it for irrigation etc.
However, there is also the past example of Chanute, kansas, that suffered a drought back in the 50s, and apparently had to recycle the exact same water some 5 to 18 times, all with 50s era technology. Mind you, I have read that the level of water treatment they achieved would not be considered acceptable today.
But. The thing is, they didn’t and couldn’t do any sort or segregation of the water streams, e.g. sewage from greywater and drinking water from everything else. Plus there was water from many people mixed together and distributed to everyone, a major risk for outbreaks of disease, and there was probably some industrial waste and people flushing pharmaceuticals down the toilet etc. A home based system can correct all those weaknesses, especially in a tinyhouse, where you probably don’t have very many people living there.
I did find one example of a guy in malta who had rigged up his house to treat the wastewater back to potable water, apparently, by the name of Marco cremona, who has a blog somewhere. Maybe you can dig it up again from this page here (which itself details an interesting project): http://www.goodentrepreneur.com/The-Competition/Entries-Pool/Sustainable-Water-Recycling-for-Hotels-Large-Commercial-Buildings-and-Small-Communities
The page is about a system that recycles sewage to potable recycling for a hotel, but he says stuff about the system he set up for his own home, too.
Whether he did the segregating of the different water streams, I don’t know. He does, however, point out on that page the issues with monitoring the quality of the water on a small scale, the sensors and so on could be hard to obtain or too expensive. However, if we look at something like the life saver bottle (or jerrycan), or the lifestraw, or the HTI hydrowell and related products, which can render even the nastiest, most dangerous water drinkable, it is clear that there is technology out there capable of ensuring the water is pathogen free. Putting more than one of these in series would produce an even more reliable system. Straying from the immediate do-it-yourselfer-able realm, there are also some pretty amazing sensing technologies like cheap infrared spectrometers and microfluidics coming out now that could help a great deal with assuring the water is pathogen free, I bet. When it comes to dissolved contaminants, I’m pretty sure there is nothing in sewage in concentrations so dangerous as to cause a major threat to life and health if you were exposed to it, even in drinking water, never mind the shower, unless maybe there were bacterial toxins or other biological (algal? fungal?) toxins in the water. Which I haven’t ever heard of, anyway… Total dissolved solids sensors are cheap, and can be used to check if there is a general malfunction with the chemical contaminant removal. There are also total organic concentration sensors, as seen in that nasa paper I just blogged about, but they’re pretty expensive.
BTW, Marco Cremona’s system seems to be mainly an MBR system followed by reverse osmosis, a common combo (though there could be some activated carbon or something in there somewhere just not being mentioned).
In the reference file, there is also reference to the “komplete” (seems to be a German company), which recycles greywater back to potable and sewage back to flush the toilet, on a largish scale.
There are some water recycling (usually grey to potable, though maybe drinking it is not recommended) systems on cruise ships, too, I have noticed. They are usually mbr and reverse osmosis, but some are just RO based, while still recovering 90% of the water (some is always wasted as brine in a reverse osmosis system).
You may be wondering why the NASA system supposedly cost $250 million to do exactly what some of these systems seem to be doing on a much larger scale on a much smaller budget. Good question. I seriously doubt the nasa system cost anywhere near that. Otherwise, while the reliability of the system is of course more demanding for nasa, and as mentioned in some of the papers, they have a hard time using biological systems (which the paper says would be better than these physico-chemical systems) because of the microgravity, I don’t know how you would account for the cost difference.
I do think it’s interesting, that in some of the nasa press releases, they go on about how the system could be used here on earth some day, as if that is some sort of super futuristic idea. But water recycling is already being done on earth without NASA’s help. While I’m sure the research on the nasa system is important and valuable (especially, as mentioned, for the water quality monitoring stuff,) the reason we can’t buy this sort of system is not because of the lack of technology. It’s because of the unreasonable laws that prevent people from reusing wastewater in “potable” applications, and probably financial barriers. E.g. I bet you still have to pay the cost of getting your house hooked up to the municipal system, which in an area like mine is something like $40k.