I use a "Zero" water waste system, it push the unused water back to the hot water pipe. One major disadvantage I find is, its coll down my hot water, so I only use it to make 20G water when the dishwasher is on or when we take a bath/shower.
Also I have installed a 50 feet coiled copper pipe b4 the RO
unit fresh water inlet, so the warm/hot water dont demage the membrane. Usually makes 20G water in 4-6 hr.