How to Install an RO System: Installing a reverse osmosis system is one of the most effective ways to add dedicated drinking-water filtration to your kitchen. Most point-of-use RO systems are installed beneath a kitchen sink and connect to the cold-water supply, drainpipe, and a dedicated drinking-water faucet.

A typical reverse osmosis system uses pressure to push water through a semipermeable membrane, producing treated water for drinking while sending concentrated wastewater to the drain. RO systems are commonly installed as point-of-use systems serving a single fixture. (US EPA)

While installation steps vary by manufacturer and system design, many under-sink RO systems follow a similar process. This guide explains how to prepare for installation, connect the major components, start the system, and check for common problems.

Important: Always follow the installation manual included with your specific RO system. The instructions in this guide are general and should not replace manufacturer requirements, local plumbing codes, or professional advice.

For ongoing maintenance after installation, visit our complete Reverse Osmosis Maintenance Guide.

Table of Contents

1. What Is an RO System?
2. Before You Install an RO System
3. Tools and Materials You May Need
4. Choose the Right Installation Location
5. Step 1: Shut Off the Cold Water Supply
6. Step 2: Install the Feed Water Adapter
7. Step 3: Install the RO Faucet
8. Step 4: Install the Drain Connection
9. Step 5: Mount the RO System
10. Step 6: Install the Storage Tank
11. Step 7: Install Filters and the RO Membrane
12. Step 8: Connect the RO Tubing
13. Step 9: Turn On the Water Supply
14. Step 10: Flush the RO System
15. Step 11: Check for Leaks
16. Common RO Installation Problems
17. How Long Does It Take to Install an RO System?
18. Should You Install an RO System Yourself?
19. RO System Installation Checklist
20. What to Do After Installing Your RO System
21. Final Thoughts

What Is an RO System?

A reverse osmosis system is a point-of-use water treatment system that typically connects to a single drinking-water fixture.

The basic treatment process uses water pressure to force water through a semipermeable membrane. The process separates treated water, often called permeate, from concentrated reject water that is directed to a drain. (US EPA)

A typical under-sink RO system may include:

• Sediment prefilter
• Carbon prefilter
• Reverse osmosis membrane
• Post-carbon filter
• Water tubing
• Feed-water connection
• Drain connection
• Dedicated RO faucet
• Storage tank on traditional systems

Tankless RO systems may have a different configuration and may not require a storage tank.

Before You Install an RO System

Before opening the box or disconnecting plumbing, take time to inspect your installation location.

Most residential point-of-use RO systems are installed beneath a kitchen sink because the location provides convenient access to:

• A cold-water supply line
• A sink drainpipe
• Space for the RO system
• A location for a dedicated drinking-water faucet

Point-of-use RO systems are generally designed to treat water at a single fixture rather than supplying filtered water throughout an entire home. (US EPA)

Check Your Available Space

Measure the space under your sink before installation.

Make sure you have enough room for:

• The RO filtration unit
• Filter replacement access
• The storage tank, if included
• Water tubing
• Drain connections

Do not install the system where routine filter replacement will be unnecessarily difficult.

Check Your Water Pressure

RO systems require adequate incoming water pressure to operate properly.

Check the manufacturer’s specifications for:

• Minimum water pressure
• Maximum water pressure
• Recommended operating pressure

If your home’s water pressure is below the manufacturer’s requirements, you may need a system designed for low-pressure applications or an appropriate booster pump.

Review Your Water Quality

Before choosing an RO system, identify the contaminants you are trying to reduce.

NSF recommends starting with your local Consumer Confidence Report for municipal water or independent water testing for private wells. You can then select a treatment system based on the contaminants of concern and the product’s specific certified reduction claims. (NSF)

Not every RO system has the same contaminant-reduction claims.

Look for systems with relevant certifications and verify the specific contaminants listed for the exact model you are considering. NSF/ANSI 58 is the primary standard associated with residential reverse osmosis drinking-water treatment systems. (NSF)

Tools and Materials You May Need

The tools required depend on your RO system and existing plumbing.

Common tools include:

• Adjustable wrench
• Phillips screwdriver
• Flat-head screwdriver
• Drill
• Drill bits
• Utility knife or tubing cutter
• Measuring tape
• Bucket
• Towels
• Safety glasses

Your RO system may include:

• Feed-water adapter
• Faucet assembly
• Drain saddle
• Tubing
• Filter cartridges
• RO membrane
• Storage tank valve
• Mounting hardware

Tip: Review the manufacturer’s parts list before beginning installation. Do not assume that fittings or adapters are interchangeable between systems.

Choose the Right Installation Location

For most homeowners, the area beneath the kitchen sink is the most practical location.

Before installing the system, confirm that you have:

✓ Access to the cold-water line
✓ Access to a suitable drainpipe
✓ Enough cabinet space
✓ Room to replace filters
✓ Space for the storage tank, if applicable
✓ A location for the RO faucet

Avoid placing the system where:

• Tubing could become kinked
• Filters cannot be accessed
• Components could be exposed to freezing temperatures
• Electrical components could be exposed to excessive moisture
• The system could interfere with cabinet doors or plumbing

Step 1: Shut Off the Cold Water Supply

Before disconnecting any plumbing:

1. Locate the cold-water shutoff valve beneath the sink.
2. Turn the valve clockwise to shut off the water supply.
3. Open the kitchen faucet to relieve pressure in the line.
4. Place a towel or bucket beneath the plumbing connection.

Confirm that the water is completely shut off before continuing.

Safety Tip: If the shutoff valve does not operate correctly or begins leaking, stop the installation and consider contacting a plumber.

Step 2: Install the Feed Water Adapter

The RO system needs a connection to the incoming cold-water supply.

The exact installation method depends on the plumbing configuration and the feed-water adapter included with your system.

The general process may include:

1. Disconnecting the cold-water supply line.
2. Installing the RO feed-water adapter.
3. Reconnecting the original faucet supply line.
4. Connecting the RO system feed tube.

Make sure all threaded connections are installed according to the manufacturer’s instructions.

Important Considerations

• Connect the RO system to the cold-water supply unless your manufacturer specifically instructs otherwise.
• Do not overtighten fittings.
• Inspect washers and seals before reconnecting plumbing.
• Make sure the feed-water valve is accessible for future maintenance.

Step 3: Install the RO Faucet

Traditional under-sink RO systems usually use a dedicated drinking-water faucet.

Your sink may already have an unused mounting hole.

If not, installation may require:

• Using an existing accessory hole
• Removing an unused soap dispenser
• Drilling a new hole if appropriate for the sink material

Before Drilling

Confirm:

• The sink material
• The faucet hole diameter required
• The location of plumbing beneath the sink
• Whether drilling could damage the sink or countertop

Some materials, including certain stone and composite countertops, may require specialized tools or professional installation.

Once the opening is prepared:

1. Insert the RO faucet.
2. Install the mounting hardware.
3. Tighten according to manufacturer instructions.
4. Connect the appropriate RO tubing.

Do not overtighten the faucet mounting hardware.

Step 4: Install the Drain Connection

Traditional RO systems produce reject water that needs to be directed to the drain.

The installation method may use a drain saddle or another manufacturer-approved drain connection.

EPA describes typical point-of-use RO systems as producing treated water while sending concentrate or reject water to the drain. (US EPA)

The general process may include:

1. Selecting the correct drainpipe location.
2. Cleaning the outside of the drainpipe.
3. Installing the drain saddle according to manufacturer instructions.
4. Creating the required opening if instructed.
5. Connecting the RO drain tubing.

Important Drain Installation Tips

• Follow the manufacturer’s recommended drain location.
• Do not install the drain connection in an unauthorized location.
• Ensure tubing is not kinked.
• Confirm that the drain connection is secure.
• Check the drain connection for leaks during startup.

Local plumbing codes may affect how drain connections are installed.

Step 5: Mount the RO System

Some RO systems are designed to sit directly on the bottom of the cabinet, while others are mounted to the cabinet wall.

If your system requires mounting:

1. Position the system.
2. Mark the mounting locations.
3. Confirm that filters can be accessed for replacement.
4. Install mounting hardware.
5. Secure the RO system.

Make sure there is sufficient clearance below the system if filter housings need to be removed.

Step 6: Install the Storage Tank

Traditional RO systems store filtered water inside a pressurized storage tank.

Tankless systems do not use a traditional storage tank.

For a traditional system:

1. Position the storage tank in an accessible location.
2. Install the tank valve according to the manufacturer’s instructions.
3. Connect the appropriate water line.
4. Keep the tank valve in the position recommended during system startup.

EPA notes that storage tanks are commonly used in point-of-use RO systems so treated water is readily available when dispensed from the faucet. (US EPA)

Make sure the tank can be accessed for future maintenance.

Step 7: Install Filters and the RO Membrane

Depending on your system, filters and the RO membrane may already be installed.

If they are not:

1. Identify each filter stage.
2. Remove protective packaging.
3. Install filters in the correct order.
4. Install the RO membrane according to the manufacturer’s instructions.
5. Confirm that filters are fully seated.

A typical RO system may include multiple prefilters, an RO membrane, and a postfilter. The exact configuration varies by model. (US EPA)

Important: Follow the Correct Filter Order

Installing filters in the wrong location can affect:

• Water flow
• System performance
• Filter life
• Membrane protection

Use the labels and installation diagram provided by your manufacturer.

Step 8: Connect the RO Tubing

RO systems use separate tubing for different water paths.

Depending on the system, tubing may connect:

• Cold-water supply → RO system
• RO system → storage tank
• RO system → RO faucet
• RO system → drain

Tips for Connecting RO Tubing

Before inserting tubing into quick-connect fittings:

• Cut tubing straight.
• Remove damaged ends.
• Make sure tubing is clean.
• Push tubing completely into the fitting.
• Pull gently to confirm the connection is secure.

Avoid:

• Kinked tubing
• Sharp bends
• Excessively long tubing
• Tubing placed where it can be crushed

Important: Follow the tubing diagram included with your RO system. The tubing configuration can vary significantly between manufacturers.

Step 9: Turn On the Water Supply

After all components are connected:

1. Check that all fittings are secure.
2. Confirm the RO faucet is installed.
3. Confirm filters are properly seated.
4. Confirm the drain connection is secure.
5. Slowly turn on the cold-water supply.

Do not immediately walk away.

Inspect the entire system while water pressure is restored.

Check:

• Feed-water connections
• Filter housings
• Tubing fittings
• Storage tank connections
• Faucet connections
• Drain connections

If you discover a leak, shut off the water and correct the problem before continuing.

Step 10: Flush the RO System

New RO filters and membranes often require flushing before normal use.

The correct startup procedure depends on the manufacturer.

Follow your system’s instructions regarding:

• Initial flushing
• Storage tank filling
• Tank draining
• Number of flushing cycles
• When water is ready for drinking

Do not assume that every RO system follows the same flushing schedule.

Why Flushing Is Important

The startup process can help:

• Remove manufacturing residues
• Flush carbon fines
• Prepare filters for operation
• Confirm normal water flow

Some RO membranes and systems may have specific flushing requirements. Manufacturer documentation should always control the final startup procedure. (US EPA)

Step 11: Check for Leaks

After installation, carefully inspect every connection.

Check for leaks:

Immediately After Installation

• Feed-water adapter
• Filter connections
• Tubing fittings
• Storage tank
• RO faucet
• Drain connection

Again After the System Runs

Check the system again:

• After the first hour
• After the storage tank fills
• After the first flushing cycle
• The following day

Even a small leak can cause significant damage if it goes unnoticed beneath a kitchen sink.

Common RO Installation Problems

Most installation problems are caused by a small number of issues.

Problem: Water Is Leaking From a Connection

Possible Causes

• Tubing is not fully inserted.
• Tubing is cut unevenly.
• A fitting is loose.
• An O-ring is damaged.
• A filter is not properly seated.

What to Do

Shut off the water supply and inspect the connection according to the manufacturer’s instructions.

Problem: Little or No Water Comes From the RO Faucet

Possible Causes

• Storage tank has not filled.
• Water supply valve is closed.
• Tank valve is closed.
• Filter is improperly installed.
• Tubing is kinked.
• Incoming water pressure is insufficient.

Traditional RO systems may take several hours to produce and store enough treated water after initial installation.

Problem: The System Produces Water Very Slowly

Possible Causes

• Low incoming water pressure
• Cold incoming water
• Restricted prefilters
• Membrane issues
• Kinked tubing

Before replacing components, confirm that the system has been given enough time to complete its initial production cycle.

Problem: Water Continues Going to the Drain

Traditional RO systems discharge concentrate water during treatment.

However, continual drain discharge after the storage tank should be full may indicate a malfunction.

EPA notes that continuous discharge to the drain can be a sign that an automatic shutoff device requires replacement. (US EPA)

Refer to your manufacturer’s troubleshooting instructions before replacing components.

How Long Does It Take to Install an RO System?

Installation time depends on:

• System design
• Plumbing experience
• Cabinet accessibility
• Existing faucet holes
• Plumbing modifications
• Whether drilling is required

For a straightforward under-sink installation, an experienced DIY homeowner may complete the work in a few hours.

However, installation can take longer when:

• A new faucet hole is required
• Plumbing needs modification
• Cabinet space is limited
• Existing plumbing is damaged
• Professional installation is required

Allow additional time for system flushing and initial water production.

Should You Install an RO System Yourself?

Many homeowners can install an under-sink RO system themselves.

DIY installation may be appropriate if you:

• Have basic plumbing skills
• Understand how to shut off the water supply
• Can follow detailed manufacturer instructions
• Have easy access to plumbing
• Are comfortable using basic tools

Consider hiring a professional if:

• Plumbing modifications are required
• You need to drill through difficult materials
• Your water shutoff valve is damaged
• You are uncomfortable working with plumbing
• You cannot access the required plumbing connections
• Local plumbing requirements apply

If you’re considering professional installation, see our upcoming guide:

Hiring a Plumber to Install an RO System

RO System Installation Checklist

Use this checklist before and after installation.

Before Installation

☐ Read the manufacturer’s instructions
☐ Check cabinet space
☐ Verify access to the cold-water line
☐ Verify access to the drainpipe
☐ Check water pressure requirements
☐ Review water quality concerns
☐ Confirm filter and membrane installation
☐ Gather required tools

During Installation

☐ Shut off the cold-water supply
☐ Install the feed-water connection
☐ Install the RO faucet
☐ Install the drain connection
☐ Position or mount the RO system
☐ Install the storage tank, if applicable
☐ Install filters and membrane
☐ Connect all tubing

After Installation

☐ Slowly turn on the water supply
☐ Check all connections for leaks
☐ Follow the manufacturer startup procedure
☐ Flush the system as instructed
☐ Check water production
☐ Check the storage tank, if applicable
☐ Inspect the system again after several hours
☐ Record the installation date

What to Do After Installing Your RO System

Installing the system is only the first step.

Proper maintenance is important for maintaining water quality and system performance.

EPA states that proper use and maintenance are critical to effective RO system function. General maintenance needs can include filter replacement, membrane replacement, storage tank maintenance, and inspection when low production, low pressure, or unexpected taste or odor occurs. (US EPA)

After installation, create a maintenance schedule for:

• Sediment filters
• Carbon filters
• RO membrane
• Postfilters
• System sanitization
• Leak inspections

Replacement schedules vary by manufacturer and water quality. NSF recommends following the replacement requirements for your specific treatment system and verifying the correct replacement components. (NSF)

For a complete maintenance schedule and troubleshooting guide, visit:

Reverse Osmosis Maintenance Guide

Our pillar guide covers:

• Filter replacement schedules
• RO membrane replacement
• Sanitizing an RO system
• Fixing low water pressure
• RO storage tank troubleshooting
• Repairing leaks
• Fixing noisy systems
• RO water taste problems
• Winterizing an RO system

Related Revosmo Guides

As the Silo 6 content cluster expands, link this article to the following supporting resources:

Installation

• DIY RO System Installation
• Hiring a Plumber to Install an RO System

Maintenance

• RO Filter Replacement Schedule
• RO Membrane Replacement
• How to Sanitize Your RO System
• Fixing Low Water Pressure in an RO System
• RO Tank Troubleshooting
• How to Fix a Leaking RO System
• How to Fix a Noisy RO System
• RO Water Taste Problems
• How to Winterize an RO System

Each of these articles should also include a contextual link back to the Reverse Osmosis Maintenance Guide to strengthen the Silo 6 internal linking structure.