The Basic Parts of a RO System (with Pictures)

Before reading our articles about how an RO system works and why it’s the best choice for water purification, let’s get to know the insides of the system first. What are they made of? Let’s check its parts.

Automatic Shut-Off Valve (SOV)

This RO system feature aims to conserve water by closing the valve automatically once the storage tank is full. It hinders the any more water from going into the membrane, and it also impedes flow to the drain. The SOV opens to send the safe drinking water through the membrane once the water is drawn from the RO faucet and the tank’s pressure falls.

Check Valve

Located at the outlet end of the membrane housing, the check valve hampers the backward flow of permeate water from the storage tank. FYI, a backward flow could fracture the RO membrane which isn’t something you’d like.

Cold Water Line Valve

This valve, which fits onto the water supply line, contains a tube that fixes to the inlet side of the RO system’s pre-filter. In short, it’s the source of water for the RO system.

check valve


Drain line

Running from the outlet end of the RO membrane housing down to the drain, the drain line is utilized to discard the water which contains contaminants and impurities that have been rejected by the RO membrane.

Flow Restrictor

This component regulates the water which flows through the RO membrane. Its purpose is to keep the flow rate needed to acquire the highest quality drinking water which is based on the gallon capacity of the RO membrane. The flow restrictor is also a great help in maintaining pressure on the entry side of the membrane. Without it, only a little drinking water would be generated because all the entering water would take the trail with least resistance and merely flow down the drain line.


The water that comes from the cold water supply line will approach the RO pre-filter first. Click the link to learn more about the types of water purification systems filters. These pre-filters get rid of salt, dirt, and other contaminants that could block the system.

BACOENG 5-Stage Ultra-Filtration Under-Sink


The treated water, after leaving the RO storage tank, will then pass through a final post-filter before proceeding to the RO faucet. Usually a carbon filter, the post-filter removes any remaining odor and taste from the permeate or product water.

RO Faucet

This is the faucet that comes with your RO system. RO systems usually use non-air gap models.

RO Membrane

The RO Membrane is to the RO system as the heart is to man. In short, it is the most important part of the system. It’s tailored to remove contaminants and pollutants. The water, after passing through this component, proceeds to a pressurized storage tank where the product or treated water is stored.

semipermeable membrane

Storage Tank

The most common RO storage tanks can hold two to four gallons of water. Thanks to the bladder located inside the tank, the water remains pressurized in the reservoir when it’s full. RO tanks are typically 15 inches tall and 12 inches in diameter.