4-Stage Reverse Osmosis System Diagram

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Curious to know what a 4-stage reverse osmosis system might look like under your sink?

Check out our helpful diagram!

4-Stage Reverse Osmosis System Diagram

Check out our diagram of a 4-stage reverse osmosis system! It illustrates an under sink RO water filter featuring two pre-filter stages, a reverse osmosis membrane, a carbon post-filter, a water storage tank, and an RO faucet.

4-stage reverse osmosis system diagram

What Is a 4-Stage Reverse Osmosis System and How Does It Work?

When it comes to reverse osmosis systems, they generally consist of various components that work together. In the diagram above, we’ve outlined the typical configuration you’ll find in most 4-stage at-home systems. Just remember, your setup might have slight variations.

A 4-stage RO system simply means that you will have four stages of filtration. Each stage will remove different contaminants.

What Are the Filter Stages in a 4-Stage RO System?

Most 4-stage reverse osmosis systems will be comprised of the following:

1. Sediment Pre-Filter

Before reaching the reverse osmosis membrane, one or multiple pre-filtration stages are employed to purify water. This is crucial for ensuring the efficient functioning of the reverse osmosis system by eliminating debris that can clog the membrane as well as chemicals. Typically, a sediment pre-filter and a carbon pre-filter are utilized at this phase.

The sediment filter will remove larger bits of dirt, debris, and dust so that they won’t clog the RO membrane stage.

2. Carbon Pre-Filter

The carbon pre-filter’s primary role is to remove chlorine and its byproducts from the water. Chlorine can damage the reverse osmosis membrane, so it must be removed before the water moves through it.

3. RO Membrane

The membrane is the star of the show. It is a semipermeable membrane, meaning that it has minuscule pores that almost solely permit water molecules through and block everything else.

4. Post Carbon-Filter

The post-filter serves as the last filtration stage following water’s passage through the reverse osmosis membrane. It enhances water purity by eliminating any remaining contaminants that might have been missed in earlier stages. Also, it removes any residual taste the water might have taken on while being stored in the storage tank.

Other 4-Stage Reverse Osmosis System Components

Of course, your reverse osmosis system will contain other components aside from the filtration stages, which are:


The primary objective of the module is to create a centralized hub that connects all system components, facilitating the input and output of water.

Water Tank

One of the primary drawbacks of reverse osmosis is its slow processing speed. To address this, many setups incorporate a storage tank to retain filtered water until needed. Countertop models do not come with storage tanks, only under sink models.

Water Dispenser

A water dispenser provides easy access to purified water, typically through a dedicated faucet.

Drain Line and Saddle

This component facilitates the disposal of all the wastewater produced by the reverse osmosis system.

Water Inlet

This is the source of input water. It’s basically a connection that supplies cold water from your plumbing system.

Automatic Shut-Off Valve

Utilizing an automated shut-off valve maximizes the efficiency of your RO system and guarantees it operates only when necessary. This valve halts the system once the storage tank reaches full capacity.

Check Valve

To safeguard the system from potential damage, the implementation of a check valve is vital as it obstructs any possible backflow of water from the storage tank or drain line.

Flow Restrictor

The flow restrictor regulates the wastewater rate, ensuring the RO system maintains adequate pressure for water to pass through the membrane.


Tubing is utilized at multiple junctures within the system to establish connections between its components.


Fittings are crucial for ensuring secure connections and preventing any leaks.

under sink reverse osmosis system

How to Install a 4-Stage Reverse Osmosis System

Tools and Supplies:

  • Electric drill capable of drilling through your sink
  • Drill bits
  • Screwdriver
  • Wrench
  • Plastic tubing cutter
  • Teflon tape
  • Hammer


  1. Create a hole in the countertop to install the faucet.
  2. Connect the drain saddle to the sink drain line, far from the dishwasher and garbage disposal lines.
  3. Under the sink, turn off the water supply. Open the kitchen faucet. Install the feed valve and reconnect the tubing.
  4. Position the RO system module.
  5. Attach the storage tank by wrapping its threaded port with Teflon tape and screwing on the connector.
  6. Follow the color coding to connect 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 any leaks.
  9. Flush the system.
  10. Close the RO faucet and open the valve for the storage tank.
  11. Fill up the tank, drain it, and repeat a few times.

If you have any questions about our 4-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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