Waterdrop Reverse Osmosis Water Filtration System, Tankless, 400 GPD Fast Flow, 1:1 Pure to Drain, model WD-G2-W
1 gallon of waste water per 1 gallon of RO - much better than most other units. I'm planning to get a booster pump to kick my water pressure up to 80 psi. If it really does 400 gallons per day, that amounts to 16.67 gallons per hour (or run for an hour and fifteen minutes every other day to make enough water for my plant collection). I can have it dump the RO water into a 5-gallon bucket, then haul it outside and pour it into a rain barrel. My tap water runs 120-150 PPM, so the filter won't have to work very hard to bring the mineral level down.
For another $60, I could upgrade to this model:
Waterdrop RO Reverse Osmosis System, 600 GPD, 2:1 Pure to Drain, Tankless, model WD-G2P600-W
It's rated at 600 gallons per day and makes just 1 gallon of waste water per 2 gallons of RO.
This looks very promising. Does anyone have any experience with this brand?