I had a SpectraPure DWS (Drinking Water System) back when I lived in Michigan because I had pretty bad well water. When I moved I broke it down and packed it away. Just a few months ago I found it in a box, cleaned and sanitized everything, changed out the carbon filter and ran it to see if the membrane was still good.
Amazingly it still works great, 5ppm water measured with my TDS meter. I built a reservoir and use it to generate all of my brewing water now.
I guess the membrane must have stayed wet enough that it didn't stop working completely. Maybe there is more waste water now than before. I should measure the quantity so whenever I end up replacing the RO membrane I can see if the waste water quantity goes down.
This is the only RO system I've ever owned so I can't really say how it compares to others