I actually run 3 membranes in series but my tap water tds is not bad. Plus I have a controller on my system that opens a solenoid to bypasses the restriction for a minute every 30 minutes of run time.I think thats because its filtered by carbon blocks + sediment filter.
Waste water still goes though the first 2-3 stages in a RO setup.
I still think if you want to save water, running a dual RO membrane in Serial config will probably save the most, but at the cost of the second membrane wearing out quickly, and you'll probably want to flush the membranes each time you finished collecting your massive amount of water.
I would of said before that doing this is probably more expensive then the waste water, however, if you look at some locations like California for example, water is ***** expensive, and Amazon has pretty cheap RO Membranes, so you may actually save some money in the long run sacrificing the longevity of one of your RO membranes.
LOL, i collected my waste water on my intial build to use to leak test my tank.
Worked out pretty well.
Then i used the water to dump it on my lawn after leak testing was done.
But rolling out a 44G Brute tub 100ft or so, even on furnature movers is a work out.
I run 3 membranes to speed up production rate instead of trying to conserve water.