A five stage reverse osmosis diagram looks more complicated than the system is, because it shows two separate water paths overlaid on one drawing: the treatment path from the supply through the membrane to the tank, and the delivery path from the tank back through a final filter to the tap. Once you separate those, the rest follows.
The five stages in order
Stage one is a sediment cartridge, catching grit and rust so nothing abrasive reaches what follows. Stages two and three are carbon, usually a granular carbon and then a carbon block, whose job is removing chlorine before the membrane, since chlorine destroys the thin film composite material quickly. Stage four is the membrane itself, where the actual reverse osmosis happens. Stage five is a small polishing carbon cartridge on the outlet of the storage tank, which removes any taste the tank has imparted during storage.
The two outputs from the membrane
This is the part diagrams handle badly. The membrane has one inlet and two outlets. Permeate, the treated water, goes forward to the storage tank. Concentrate, the reject stream carrying the rejected dissolved solids, goes to the drain through a flow restrictor. The restrictor is what maintains pressure across the membrane, and a system running with no restrictor or a wrong one either sends most of the water to waste or fouls the membrane. On the diagram it is the small component between membrane and drain saddle.
Tank, faucet and the delivery path
The tank is a pressure vessel with a bladder and an air charge behind it, because the membrane produces water far too slowly to serve a tap directly. It fills from the membrane and discharges when the dedicated faucet opens. On the diagram, note that the tank connects through a single tee: the same line fills and empties it. The polishing filter sits between tank and faucet, so every glass passes through it on the way out, which is why an empty tasting system is often a spent stage five rather than a failed membrane.
The valves the diagram also shows
Two small components are easy to overlook and cause most of the puzzling faults. The automatic shutoff valve senses tank pressure and stops production when the tank is full, so a failed one leaves the system running to drain permanently. The check valve on the membrane permeate line stops tank water flowing backwards through the membrane, and a failed one produces a system that never fills. There is also a tank isolation valve, and leaving it closed after servicing is the single most common cause of no water at the faucet. Our reverse osmosis guide covers commissioning.
Questions people ask about 5 stage reverse osmosis system diagram
What are the five stages?
Sediment, then two carbon stages, then the membrane, then a polishing carbon filter between the storage tank and the dedicated faucet.
Why is carbon before the membrane?
Chlorine destroys thin film composite membrane material quickly, so it must be removed before the water reaches the membrane.
What is the flow restrictor for?
It maintains pressure across the membrane by limiting the reject stream. Without the right one the system either wastes water or fouls quickly.
The system stopped producing water, where do I look?
The tank isolation valve first, then the automatic shutoff valve and the permeate check valve, which cause most puzzling production faults.