3-Stage Reverse Osmosis System Diagram

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A 3-stage reverse osmosis system is the minimum for effective RO filtration.

Let’s look at its setup with our helpful diagram!

3-Stage Reverse Osmosis System Diagram

Take a look at our 3-stage reverse osmosis system diagram, featuring an under sink RO water filter equipped with a carbon pre-filter, the reverse osmosis membrane, a carbon post-filter, a water storage tank, and the RO faucet.

3-stage reverse osmosis system diagram

How Does a 3-Stage Reverse Osmosis System Work?

A 3-stage reverse osmosis system employs a sequence of filters through which the water passes. Each filtration stage eliminates specific components from the water, and collectively, they work together to achieve a contaminant reduction rate of over 99%.

  • First, water from the cold water supply under your sink enters the carbon pre-filter stage. Here, chlorine, sediment, and chemicals are removed.
  • Next comes the reverse osmosis membrane which removes most of the contaminant load.
  • Then, the water flows into the storage tank or directly to the carbon post-filter if someone’s opening the RO faucet.
  • The wastewater rejected by the RO membrane flows along the drain line and directly into the sink drain.

3-Stage Reverse Osmosis System Components

3-stage reverse osmosis systems consist of multiple components working together. In the diagram, we have provided the typical configuration found in most home-use systems. Please note that your specific situation may vary.

The Filter Stages

A 3-stage RO system is called so because it has three filter stages. Those are usually:

Carbon Pre-Filter

A carbon pre-filter, whether in the granular activated carbon or carbon block form, will eliminate elements in water that cause undesirable tastes and odors. Its main objective is to eliminate chlorine, preserving the RO membrane’s integrity.

RO Membrane

The key component of a reverse osmosis filtration system is the RO membrane, which effectively eliminates dissolved solids and harmful contaminants like heavy metals and other chemicals.

Carbon Post-Filter

Stage 3 serves as a secondary activated carbon post-filter, enhancing water purification, particularly after storing it in a tank. This will also help improve the water’s taste.

Other Components

Aside from the filtration stages, a reverse osmosis system contains various other components.


The module serves as a central hub, facilitating the connection of various system components. It offers inputs, outputs, and threaded connectors for easy integration.

Water Tank

One drawback of reverse osmosis is its slow speed. To address this, many setups incorporate a storage tank to store filtered water until needed. However, it’s essential to avoid making the tank excessively large as it can lead to some drawbacks of its own. For instance, water may acquire a stagnant taste if it remains in the tank for an extended period.

Water Dispenser

Most RO systems have a separate faucet to dispense water. This faucet is usually installed into the sink near the main faucet.

Drain Line and Saddle

This section enables the reverse osmosis system to eliminate all the wastewater it produces.

Water Inlet

This is the source of input water. It’s merely a connection for the cold water supply in your plumbing system.

Automatic Shut-Off Valve

An ASO valve will maximize the efficiency of your RO system and guarantee that it operates only when necessary. This valve shuts off the system as soon as the storage tank reaches capacity.

Check Valve

This valve effectively obstructs the backflow of water from the storage tank or drain line, preventing any potential damage to the RO membrane.

Flow Restrictor

The flow restrictor regulates the wastewater rate, guaranteeing that the RO system maintains sufficient pressure for water to pass through the membrane effectively.


Tubing is utilized at different stages of the system to establish connections between its components.


Fittings are vital to ensure secure connections and prevent any potential leaks.

How to Install a 3-Stage Reverse Osmosis System

under sink reverse osmosis system

If you want to DIY your 3-stage reverse osmosis system installation, it’s completely doable. Instructions:

  1. Creating a hole in your countertop for installing the faucet.
  2. Attach the drain saddle to the sink drain line away from the dishwasher and garbage disposal lines.
  3. Turn off the water supply beneath the sink, then open the kitchen faucet. Install the feed valve and reconnect the tubing.
  4. Position the RO system module.
  5. Connect the storage tank by wrapping Teflon tape around its threaded port and screwing on the connector.
  6. Link the tubing to the feed water valve, tank valve, and other components.
  7. Install all filter cartridges and the membrane.
  8. Turn on the feed water valve and check for leaks.
  9. Allow the system to flush.
  10. Close the RO faucet and open the valve for the storage tank.
  11. Fill the tank, drain it, and repeat the process.

If you have any questions about our 3-stage RO system diagram please don’t hesitate to leave a comment below!

About the Author Alexandra Uta

Alex is a content writer with an affinity for research and a methodical attention to detail. Since 2020, she has fully immersed herself into the home water treatment industry only to become an expert herself. Alex has been using water filters and similar products for years which has gained her lots of hands-on experience.
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