The reject stream cannot be eliminated, because it is what carries rejected material away from the membrane. It can, however, be reduced or put to use, and the options differ enormously in how much they achieve. Ranking them honestly is more useful than the marketing term, because two of them are real and one is a redirection that may cost you elsewhere.
A permeate pump, the genuine improvement
As the storage tank fills, its back pressure rises and works against the membrane, so a system spends much of its time producing inefficiently and sending proportionally more water to drain. A permeate pump uses the energy of the reject stream itself to push product into the tank, removing that back pressure. The result is a real reduction in the reject ratio, a faster fill, and better quality product water because the membrane is working under better conditions. It needs no electricity and is the first upgrade worth making.
Check the tank and the pressure first
Before buying anything, two free checks often improve the ratio. A storage tank with the wrong air charge makes the system work against a poorly performing tank continuously, and setting it to specification when the tank is empty can change production noticeably. And low incoming line pressure means the membrane produces slowly while the drain flows at the same rate, which makes the ratio look terrible; a booster pump on a low pressure supply improves both production and the ratio at once.
Recirculating to the hot line, and its cost
The design usually sold as zero waste returns the concentrate to the household hot water line rather than the drain. Nothing is discarded, so the claim is literally true. The consequence is that water carrying a higher dissolved mineral content than the feed is recirculated into showers, laundry and the water heater. On soft water that may be unremarkable; on hard water it means feeding progressively concentrated hardness to the appliance least able to tolerate it. Consider your hardness before buying one.
Using the reject stream deliberately
The simplest honest answer in some households is to collect and use it. The concentrate is not sewage: it is the feed water with a higher dissolved mineral content, so it is suitable for watering many plants where the source water is not saline, for cleaning, or for flushing. That requires a container and a habit rather than equipment. What is never a good idea is restricting the drain line to reduce the flow, which fouls the membrane quickly and costs far more than it saves. Our whole house RO guide covers the larger scale question.
Questions people ask about zero waste reverse osmosis
Can the reject stream be eliminated?
No. It is what sweeps rejected material off the membrane. It can be reduced or reused, but not removed.
What genuinely reduces the ratio?
A permeate pump, which removes storage tank back pressure using the reject stream's own energy, plus correcting tank air charge and low line pressure.
Is recirculating to the hot line a good idea?
It depends on your hardness. It feeds concentrated minerals to the water heater, which is the appliance least tolerant of scale.
Can I just restrict the drain line?
No. That fouls the membrane quickly, and replacing it costs far more than the water saved.