How to Install a 4-Stage Reverse Osmosis System

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A 4-stage reverse osmosis system employs four filtration steps to deal with water contamination.

Those steps include a sediment pre-filter, a carbon pre-filter, the RO membrane, and a carbon post-filter.

Today, we will show you how you can install such a system at home!

Key Takeaways

Here is how to install a 4-stage reverse osmosis system:

  1. Install the faucet by drilling a hole in the countertop or sink and positioning it for maximum convenience.
  2. Install the drain saddle on the sink drain line, positioning it above and at a distance from the dishwasher discharge and garbage disposal.
  3. Turn off the supply of cold water below your sink.
  4. Relieve pressure in the water lines by opening the faucet.
  5. Detach tubing from the cold water valve and install the shutoff valve.
  6. Reconnect the tubing.
  7. Position the storage tank within your kitchen sink cabinet. Apply Teflon tape to the threaded port located at the top. Attach the tank valve/connector.
  8. Mount and connect the RO module using color-coded tubing.
  9. Install the filter elements.
  10. Open the feed water valve and the RO faucet, checking for leaks.
  11. Flush the system to remove debris.
  12. Close the RO faucet and open the storage tank valve.
  13. Allow the tank to fill and drain 2-3 times.

4-Stage RO System Diagram

First of all, this 4-stage reverse osmosis system diagram should help to give you a general idea of what the setup should look like.

under sink reverse osmosis system diagram

How to Install a 4-Stage Reverse Osmosis System

So, how do you install a 4-stage reverse osmosis system?

Installing a 4-stage reverse osmosis system yourself is easy enough if you are armed with the right tools and a good set of instructions. So, we have put together the instructions for you!

Mind you, these instructions are specific to a 4-stage reverse osmosis system, with one sediment pre-filter, one carbon pre-filter, the RO membrane, and one carbon post-filter.

1. Faucet Installation:

  1. Determine if a new hole must be drilled in the sink or countertop. Use a special drill bit for certain materials to prevent scratching or chipping. Start with a pilot hole if a larger hole is needed.
  2. Insert the faucet through the hole and secure it from the bottom using washers and a nut. Attach the fitting and tighten it with a wrench.

2. Drain Saddle Installation:

  1. Make a ¼ inch opening in the top or side of the drain pipe and securely attach the drain clamps with bolts. Take care not to tighten them too much. To prevent clogging and contamination, ensure that the saddle is above and away from the dishwasher discharge and garbage disposal. It should be at least six inches higher than the p-trap.

3. Feed Valve Installation:

  1. Turn off the cold water supply and release pressure in the water line by opening the faucet.
  2. Disconnect the tubing from the cold water valve and install the new feed valve, tightening it securely with a wrench. Close the feed valve.
  3. Connect the cold water tubing of your existing faucet back to the new valve, using an adapter if necessary. Turn the water supply back on.

4. Storage Tank Installation:

  1. Position the water storage tank within 10 feet of the new faucet for proper water pressure.
  2. Wrap Teflon tape around the threaded port at the top of the tank. Attach the tank valve or tank connector by hand-tightening.
  3. The storage tank can also be placed horizontally in many systems without affecting filtration performance, which is useful when space is limited.

5. Mount and Connect the RO Module with Tubing:

  1. Use color-coded tubing with quick-connect fittings to connect the RO module. Push the tubes as far as possible and ensure they are securely connected.
  2. Attach the supply line to the feed water valve and the feed port of the RO module. Adjust the line length to avoid kinks.
  3. Connect one line to both the tank valve and the outlet port of the filter system.
  4. Connect another line to the drain saddle and the flow restrictor of the RO module, cutting the line if necessary.
  5. Connect the final line to the RO faucet and the post-filter outlet port.

6. Filter and Membrane Installation:

  1. Unscrew the filter housings and insert the sediment and carbon pre-filters. Screw the housings back on and tighten them with a filter wrench.
  2. Install the RO membrane by removing the housing cap and inserting the cylinder into the socket. Replace the cap to ensure a snug fit.
  3. Install the carbon post-filter by attaching the tubing into the inlet port.

7. Start the System:

  1. Open the feed water valve and the RO faucet while keeping the storage tank valve closed. Check for any potential leaks in the connections.
  2. After around 15 minutes, water will start dribbling out of the dispenser. It may appear slightly darker initially due to flushed-out carbon fibers. Close the faucet and open the storage tank valve to fill the tank.
  3. Once the tank is full, the sound of water running down the drain will stop. Open the drinking water faucet to flush the entire unit.
  4. When the water flow reduces to a dribble, it indicates that the storage tank has emptied. Close the faucet and allow the tank to refill.
  5. Some manufacturers recommend flushing a new system 2-3 times before use. Once the flushing process is complete, the setup is finished.

under sink reverse osmosis system

4-Stage RO System Components

System Module

The system module connects all the components of the RO system, including pre and post-filters, RO faucet, and storage tank. Some models may have a bracket for mounting the system module.


The pre-filters in a 4-stage RO system consist of a sediment filter to remove debris and a carbon filter to eliminate chlorine and other chemicals.

RO Membrane

The reverse osmosis membrane is the main filtration component that removes contaminants that have bypassed the pre-filters. It works by applying pressure to separate impurities and dissolved solids from the water. The pure water passes through the membrane to the storage tank, while the impurities are flushed away with wastewater.


After leaving the storage tank, the RO-filtered water goes through the carbon post-filter. This filter eliminates any unpleasant tastes or odors in the water.

Bladder Tank

The pressurized tank stores the reverse osmosis water, ensuring a constant supply of filtered water whenever needed.


RO systems come with a designated faucet to provide optimal flow rate and prevent cross-contamination with regular tap water.

Drain Saddle and Drain Line

These components direct and carry the wastewater produced during filtration away from the unit for disposal. The wastewater contains the impurities that have been filtered out.

Feed Water Valve

The feed water valve connects your kitchen sink’s water supply to the RO system.

ASO Valve

The auto shut-off valve stops the water filtration system when the storage tank reaches its maximum capacity. It resumes once the tank empties.

Check Valve

The check valve prevents the backward flow of water towards the RO membrane, preventing damage.

Flow Restrictor

The flow restrictor controls water pressure within the RO membrane housing, ensuring optimal filtration effectiveness.


Multiple tubes connect all the components of the system together.


The system includes fittings and connectors that are usually color-coded for easy installation.

If you have any questions about 4-stage RO system installation 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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