Just finished setting up this RO system in an outhouse. Bought from a neighbour, they had it for treating water for tropical fish but didn’t use it for very long (didn’t have the heart to ask why). I had to re-jig some of the connections to have three pre treatment filters. Total cost with new filters £60.
Using it to treat water from our well, TDS has gone from 80 to about 3 (and that could be due to electrode contamination).