a photo of a single drain sink with a garbage disposal

Where environmental factors continually threaten the purity of our water, the significance of having access to clean drinking water can't be overstated. Among the various methods of water purification, Reverse Osmosis (RO) systems stand out for their efficiency in removing contaminants. However, the installation of an RO system can be a daunting task, especially when dealing with the unique challenges of a single drain sink. 

While RO systems are a popular choice for many households, their installation in homes with a single drain sink often poses specific challenges. Single drain sinks, as opposed to double or triple basin sinks, offer limited space and fewer options for drainage connections. This can make the installation of an RO system's drainage line slightly more complex, requiring careful planning and execution.

However, with the right tools, knowledge, and a bit of patience, you can successfully install your RO system in a single drain sink setup. This guide is designed to walk you through each step of the process, ensuring your system functions efficiently and safely.

Understanding Your Reverse Osmosis System

Before we dive into the intricacies of installation, it's crucial to have a clear understanding of how a Reverse Osmosis (RO) system works and the key components involved, particularly those related to drainage. This knowledge will not only aid in the installation process but also help in troubleshooting and maintenance down the line.

Reverse Osmosis is a filtration process that removes impurities from water by using pressure to force water molecules through a semipermeable membrane. This membrane blocks contaminants while allowing clean water to pass through, resulting in purified water on one side and wastewater, often referred to as brine or reject water, on the other.

Components of an RO System:

  1. RO Membrane: The core of the system, where the actual process of reverse osmosis occurs.
  2. Filters: Pre-filters and post-filters are used to protect the membrane and enhance water quality. These include sediment filters, carbon filters, and others.
  3. Storage Tank: Where purified water is stored for on-demand use.
  4. Faucet: A dedicated faucet typically mounted on the sink for dispensing the purified water.
  5. Pressure Regulator and Valves: These ensure the system operates under optimal pressure conditions.
  6. Drain Line: A crucial component for disposing of the wastewater generated during the filtration process.
  • The drain line in an RO system plays a pivotal role. It carries the wastewater, which includes the removed contaminants, away from the RO membrane. Proper installation of the drain line is essential to prevent issues like water backup, leaks, and damage to the system. In a single drain sink setup, this becomes even more significant due to the limited space and fewer options for connection.

Preparing for Installation

Installation of your RO system in a single drain sink requires careful preparation. This involves gathering the necessary tools and materials, along with understanding the preliminary steps that set the stage for a smooth installation process. Here's what you need to prepare:

Tools and Materials Needed

To successfully install your RO system, you will need a variety of tools and materials. Ensure you have the following items ready:

  1. Adjustable Wrench: For tightening and loosening connections.
  2. Drill with Bits: Needed for creating a hole in the sink for the faucet, if one isn't already present.
  3. Teflon Tape: Useful for securing threaded connections and preventing leaks.
  4. Utility Knife: For cutting tubing to the desired length.
  5. RO Tubing: Specific tubing provided with your RO system for water lines.
  6. Drain Saddle: An essential component for connecting the RO system drain line to your sink's drain pipe.
  7. Screwdriver: For various adjustments and installations.
  8. Bucket and Towels: Handy for catching any water spillage during installation.

Safety Precautions

Safety is paramount when working on plumbing projects. Here are some tips to ensure a safe installation process:

  • Turn Off Water Supply: Before starting, turn off the water supply to avoid any unexpected water flow.
  • Check for Electrical Hazards: Ensure there are no electrical hazards near your working area, especially if you are using a drill.
  • Wear Protective Gear: Safety glasses and gloves can protect you from sharp edges and minor accidents.

Preliminary Steps

Before starting the actual installation, it's important to complete a few preliminary steps:

  1. Clear the Area: Make sure the area under your sink is clean and clear of any items that might obstruct your access.
  2. Inspect Your Sink and Plumbing: Familiarize yourself with the plumbing layout under your sink. Identify the cold water line, which is where you'll connect the RO system for its water supply.
  3. Plan the Route for Your Tubing: Consider the most efficient and least obstructive path for running the tubing from the RO system to the faucet and drain.

Step-by-Step Installation Guide

Now that you're prepared with the necessary tools and knowledge, let's dive into the step-by-step process of installing your RO system's drain line with a single drain sink. This guide will walk you through each stage, from positioning the system to testing it.

Step 1: Positioning the RO System
  1. Locate the System: Choose a spot under your sink to place the RO system. Ensure it's easily accessible for future filter changes and maintenance.
  2. Secure the System: Some systems are designed to sit on the cabinet floor, while others may need to be mounted to the cabinet wall. Follow your system's instructions for proper placement.

Step 2: Connecting to the Water Supply

  1. Identify the Cold Water Line: Locate the cold water line under your sink; this is where you'll connect the RO system.
  2. Install the Feed Water Adapter: Turn off the cold water supply and install the feed water adapter. This will split the water line, directing water to both the sink and the RO system.
  3. Connect Tubing to the RO System: Run the tubing from the feed water adapter to the inlet port of the RO system.

Step 3: Installing the Drain Line Adapter (DLA)

  1. Select the Drain Line Location: Choose a spot on your sink's drain pipe for the DLA, ideally above the P-trap to prevent backflow.
  2. Drill a Hole for the DLA: Carefully drill a hole in the drain pipe where you've chosen to place the DLA.
  3. Attach the DLA: Secure the DLA onto the drain pipe, ensuring a tight and leak-proof connection.

Step 4: Ensuring Proper Waste Water Drainage

  1. Connect the RO Drain Line: Attach the RO system's drain line to the DLA. Make sure it's secure to prevent leaks.
  2. Check for Proper Slope: Ensure that the drain line has a downward slope towards the drain to facilitate proper wastewater flow.

Step 5: Checking for Leaks and Performing a System Test

  1. Turn On the Water Supply: Once all connections are made, turn on the water supply and check for leaks at all connection points.
  2. Flush the System: Follow the manufacturer's instructions to flush the new system, which typically involves running the system for some time to clear out any manufacturing residues.
  3. Test the Faucet: Ensure that the dedicated RO faucet is dispensing water correctly and check for any leaks.

NOTE: If the drain saddle is aligned with the garbage disposal, it may obstruct the disposal's discharge and increase the risk of water backflow into the RO system. Therefore, it's advisable to acquire a Drain Line Adapter (DLA) with a 1/4-inch Quick Connect Fitting for a Water Filter and a 7/8-inch Fitting for a Dishwasher. This approach eliminates the need to drill a hole for your drain saddle. Refer to the bellow photo to visualize how your setup will appear.

a photo of a single drain line sink set up with a drain line adapter linked to the garbage disposal and dishwasher

To install with Dishwasher:
Step One: Remove dishwasher hose from disposal and clean opening
Step Two: Mount hose coupler over exposed nipple and mount the adapter
Step Three: Cut off smaller unneeded barb sizes
Step Four: Reconnect dishwasher hose (cut to length) and insert RO drain tubing

To install without Dishwasher:

Step One: Remove knock-out plug and cut off Wye branch
Step Two: Connect Wye branch with hose coupler and insert RO drain tubing


Troubleshooting Common Issues

Even with careful installation, you might encounter some common issues with your newly installed RO system. Here's how to troubleshoot and resolve these problems:

How to Resolve Water Backflow

Water backflow in Reverse Osmosis (RO) systems can be a significant issue, potentially leading to contamination and reduced efficiency. Here are some steps to resolve water backflow problems:

  1. Check and Adjust the Check Valve:

    • The check valve in an RO system prevents the backward flow of water. Ensure that it's functioning correctly. If it's faulty or stuck, it may need to be cleaned or replaced.
  2. Inspect and Replace the Flow Restrictor:

    • The flow restrictor maintains pressure in the RO membrane and controls the flow of water. A malfunctioning restrictor can cause backflow. Check its condition and replace it if necessary.
  3. Ensure Correct Installation of Drain Line Adapter (DLA):

    • Proper installation of the DLA is crucial. It should be installed above the P-trap in your sink to prevent backflow. If it's incorrectly installed, reposition it according to manufacturer guidelines.
  4. Examine Non Air Gap Faucet:

    • Most RO system uses a non air gap faucet, ensure it's not clogged. A blocked faucet can cause backflow and leaks. Clean it to remove any obstructions.
  5. Maintain Optimal Tank Pressure:

    • Incorrect pressure in the RO storage tank can lead to backflow. The typical pressure for an empty tank is around 7-8 psi. Check the pressure with a tire gauge and adjust as needed.

Dealing with Limited Space Under the Sink

  • Problem: Not enough room to comfortably fit the RO system and its components.
  • Solution: Consider using flexible tubing to maximize space. If necessary, reorganize or remove items stored under the sink to make room for the system.

Addressing Leaks or Blockages

  • Leaks at Connection Points:

    • Tighten any loose fittings with an adjustable wrench.
    • Check and replace worn-out or improperly applied Teflon tape.
  • Blockages in the RO System:

    • Inspect the filters and membrane for clogging. Replace if necessary.
    • Ensure the tubing is not kinked or bent sharply, as this can restrict water flow.
Ensuring Compliance with Local Plumbing Codes
  • Problem: Installation requirements vary by location, and non-compliance can lead to issues with local authorities.
  • Solution: Always check your local plumbing codes before installation. If in doubt, consult a professional plumber to ensure your setup meets all regulations.

Addressing Noisy Drain Line

  • Problem: The drain line can sometimes produce a gurgling sound during the filtration process.
  • Solution: This is usually normal, but to reduce noise, you can:
    • Ensure the drain line has a gradual slope without sharp bends.
    • Check if a faucet is required or beneficial in your setup.

Handling Slow Water Production

  • Problem: RO system produces water slower than expected.
  • Solution:
    • Check if the water pressure feeding the system is within the recommended range.
    • Inspect the pre-filters and membrane for blockages or the need for replacement.

Water Hammer

A water hammer condition, also known as hydraulic shock, is a plumbing issue characterized by loud, banging noises in the pipes. This phenomenon occurs when a flow of water in the pipes is suddenly stopped or changed, causing a shockwave or pressure surge that travels through the plumbing system. Water hammer can happen in household plumbing systems and is often triggered by quickly closing valves, like those in washing machines, dishwashers, or when a faucet is rapidly turned off.

Key aspects of water hammer include:

  1. Causes:

    • Quick closing of valves.
    • High water pressure in the pipes.
    • Sudden stop in the flow of water, causing a momentum change.
  2. Effects:

    • Loud banging or knocking sounds in pipes.
    • Potential damage to pipes and fittings, possibly leading to leaks.
    • Strain on pipe supports and connections.
  3. Solutions:

    • Installing air chambers or water hammer arrestors, which absorb the shockwave.
    • Reducing water pressure if it's excessively high.
    • Securing loose pipes to prevent movement during pressure surges.
    • Gradually closing faucets and valves to avoid sudden stops in water flow.
    • Regular maintenance of appliances that quickly shut off water flow.

Maintenance Tips

Regular maintenance is crucial for keeping your Reverse Osmosis system operating efficiently and ensuring the longevity of the system. Here are some essential maintenance tips:

Regular Filter Changes
  • Sediment and Carbon Filters: These should be replaced every 6 to 12 months, depending on usage and water quality. They protect the RO membrane by removing sediment and chlorine.
  • RO Membrane: Typically, this should be replaced every 2 to 3 years. However, this depends on your water quality and how well the pre-filters are maintained.
  • Post-filters: Change these annually to ensure the final water quality is up to standard.
System Sanitization and Cleaning
  • Sanitize the System: It's recommended to sanitize your RO system annually. This involves using a sanitation kit or a solution recommended by the manufacturer.
  • Clean the Storage Tank: Periodically drain and clean the storage tank to prevent bacterial growth and maintain water freshness.
Checking for Leaks and Damage
  • Regularly Inspect for Leaks: Check all connections, especially at the filter housings and the faucet, to ensure there are no leaks.
  • Inspect for Wear and Tear: Look for signs of wear or damage in the tubing and replace if necessary.
Monitoring Water Pressure
  • Check Water Pressure: Ensure the water pressure feeding the system is within the manufacturer's recommended range. Low pressure can reduce the efficiency of the system.
  • Pressure Tank Maintenance: If your system has a pressure tank, check and adjust the air pressure if necessary.

Keeping an Eye on Water Quality

Remember that while RO systems are excellent for providing quality water, they also generate wastewater. Be mindful of water usage and consider ways to repurpose the reject water for non-potable uses like watering plants.

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