How Do You Install a Reverse Osmosis Filtration System

By purchasing a reverse osmosis system online and installing the system yourself, you can save a ton of money. That’s why we offer as many DIY resources as possible for our customers. In this blog, we will be going over how to install an undersink reverse osmosis system. Please keep in mind that if space is an issue this system can also be installed in a basement or other location. However, if this is the case a permeate pump option is recommended for added pressure. And to avoid damage, never install in a location where temperatures fall below freezing.

How Do You Install a Reverse Osmosis Filtration System

Before we start with the installation steps, let’s take a look at the tools you’ll need:

  • Adjustable Wrench
  • Drill
  • Philips Head Screw Driver
  • ¼” Drill Bit
  • 7/16” Drill Bit

Starting the Install

  1. First, let’s start with the faucet. The RO faucet should be placed near the sink where drinking and cooking water is used. A 2-inch flat surface space is required to mount the faucet. Note*: the thickness of the mounting surface should not exceed one inch and a quarter.  If the sink has a sprayer it can be disconnected for the faucet installation, if not you will have to do a manual install. Keep in mind though if you have a Granite, Quartz, or any kind of stone countertop that can crack or split, you may want to consider having a professional drill the faucet hole. 
  2. Before drilling the hole, check under the sink to make sure you have space and will not be interfering with anything like plumbing. Drill a 7/16th hole, making sure the drill bit is compatible with the surface material. Once you have your hole, you can begin mounting the faucet. 
  3. Place the base plate followed by the rubber washer onto the faucet and place it into the drilled faucet hole. The faucet should be positioned so it empties into the sink and the spout swivels freely for convenience. Underneath the sink attach the flat washer, followed by the star washer and then the Hex nut. Tighten the nut until the faucet is secure. Note* It may easier to have someone hold the faucet while you tighten the nut.
  4. Now attach the faucet adapter to the threads. Make it hand tight and then give it an extra half-turn with a wrench. Do not apply Teflon tape to this fitting.
  5. Next, you will install the Feed Water Angle Stop Valve. 
  6. Turn off the cold water supply valve for the sink faucet.
  7. Next, open the sink faucet cold water to relieve the pressure. Remove the sink faucet tubing from the shutoff valve. Be sure to have a towel to dry any water that is spilled. Now install the angle stop valve on the sink faucet shutoff valve and tighten it. Don’t worry about the angle stop valve position because it will swivel and can be positioned later. 
  8. Now install the tubing on the angle stop valve and tighten. 
  9. Be sure the blue handle on the angle stop valve is in the closed position. Now open the sink shutoff valve and check the angle stop connections for leaks. If there are leaks, repair them now.
  10. Now you can install the Drain Saddle. 
  11. Drain saddle valves are designed to be installed on a standard 1 1/2” inch PVC drainpipe. Install the drain saddle valve above the trap on the vertical or horizontal tailpiece. Never install a drain saddle valve close to the outlet of garbage disposals because it may result in the plugging of the drain line. 
  12. Position the port side of the drain saddle valve at the selected location to judge where to drill your opening. If the pipe is horizontal make sure to never position the opening at the bottom.  A side or top position is recommended.  Install the rubber gasket on this half of the drain saddle.  Be sure the gasket hole is lined up with the porthole.
  13. Drill a 1/4” hole through one side of the pipe.  BE CAREFUL not to drill through both sides of the pipe.
  14. Position both halves of the drain saddle on the drain pipe. A good tip is to use a drill bit or screwdriver to check that your drilled hole and the drain saddle port are lined up. 
  15. Secure the drain saddle clamp on the valve with the provided bolts and nuts. Make sure not to over tighten, just make it snug

How to Install Under Sink Reverse Osmosis System

Many of our customers who purchase an under-counter Reverse Osmosis drinking water filtration system choose to install the system themselves. If you’re handy and somewhat mechanical, DIY RO install should not be too difficult or time consuming.

Besides, installing the reverse osmosis system yourself can save you a bundle !

Install Reverse Osmosis Under Sink

Before you get started, make sure you have these items ready:

  • Reverse Osmosis System
  • RO storage tank
  • Faucet and Installation Kit

Tools Needed to Install a Reverse Osmosis Drinking Water System:

– Wrenches Sizes 7/16”, 9/16”, ½” & 5/8”

– Phillips Screw Driver- Drill with 3/8” Chuck

– Drill Bits Sizes ¼” or 1 1/8” For Air Gap faucet

DIY Reverse Osmosis Install Instructions


Step 1. Installation Location

Before you get started, clean out under the sink and make sure there is ample space to install the RO system. Locate the “cold” water shut off valve and sink drainpipe.

Step 2. Close the Cold Water Valve

Shut off the “cold” water supply under the sink or the location where the system will be installed. If the existing “cold” water valve is inoperable, the water supply to the house must be shut off. Once the water is shut off, relieve the line pressure by turning on the cold water faucet.

Step 3. Connect To Cold Water Line

There are several options when connecting the reverse osmosis unit to the cold-water source. They are:

A. Saddle valve (Standard) – Assemble saddle valve clamp on the “cold” water line. Turn the pipe clamp adjustment plate to fit the contour of the pipe. (Small radius for 3/8” pipe, larger radius for 7/16” through 5/8” pipe). Tighten bolt so saddle valve is firmly attached to feed water pipe (be careful not to over tighten).

B.  Ez adapter. (Optional) : Use some Teflon tape to prevent leaks. Assemble 90 degree needle valve into the feed adapter.

For “Flex line” installation: Disconnect the flex line at the sink and install the feed adapter. Reconnect the flex line to the adapter.

For “Solid line” installation: Disconnect the line at the sink cut off approximately ¾” off the line. Install the feed adapter and reconnect line to the feed adapter.

Step 4. Drain Line Connection:

NOTE: If the drain line pipe is corroded, we strongly suggest replacing it.

At a point approximately six inches above the trap, drill a 5/16” diameter bole through one wall of the pipe. Next, attach the drain clamp; making sure that the hole in the clamp is aligned with the hole in the pipe. Use a punch or drill bit to align the holes while tightening the clamp. Be careful not to over tighten the clamp.

Step 5. Install Faucet:

The faucet must be positioned with aesthetics, function and convenience in mind. An ample flat area is required for the faucet base, so the base nut can be properly tightened. Conditions may exists which eliminate the need to drill a hole in the sink.

5a. If a hole previously installed in the sink, covered by a chrome plate cover, then simply remove the cover and mount the faucet.

5b. If a spray hose that may not be functioning or needed. Remove the spray hose and plug the outlet under the main faucet. If the sprayer uses a diverter at the base of the spout remove it, as the sprayer diverter may pop up and shut the water off to the main faucet.

5c. If space is not available on the upper sink area, the faucet can be located in the counter top close to the edge of the sink. Be careful to watch for obstructions below the counter such as drawers, cabinet walls, support braces etc. If the counter top is ceramic tile the method for drilling the faucet hole is the same as for drilling a porcelain sink.

5d. The drilling process although not complicated, requires a certain amount of caution and preparation. Porcelain enameled sinks can be chipped if care is not exercised when drilling the hole for the faucet assembly. There are several ways of drilling the holes in to porcelain sinks without chipping; we have found these two methods work very well.

D.1 Using a carbide grinding wheel, grind away the porcelain where the ¼” diameter hole is to be drilled. Drill a ¼” diameter hole through the metal. This method results in a very clean and smooth hole.

D.2 Using a heavy duty variable speed drill and a carbide tip drill bit, carefully drill a ¼” diameter hole through the porcelain and metal sink.

5e. For stainless steel sinks, drill a ¼” diameter hole. Lightly file the edge of the hole to make sure it is smooth and free of any burrs. Caution: Do not allow metal chips to remain on the porcelain surface of the sink for any length of time, the metal chips will stain the sink and be very difficult to remove.

Once the hole has been drilled in the sink, the faucet stem may be inserted in the hole. Be sure the faucet body, faucet base and the rubber faucet base washer are in place above the sink.

Install the star lock washer and nut on the faucet stem under the sink and tighten firmly while aligning faucet in the desired direction. Once the faucet is installed, attach the ¼” tubing on to the bottom of the faucet stem and tighten.

Note: Some states require the use of an air gap faucet. To assure compliance check you local plumbing code. Locate the drain connection away from the garbage disposal to prevent potential contamination and system fouling.

You might also refer to our RO Troubleshooting Guide to answer common RO issues including slow water flow, noisy drain or faucet, and more. Our suggestions on what to know before purchasing a reverse osmosis system might also prove helpful.

Hire a Plumber for RO Installation

Know your limitations. If you’re worried you don’t have the right tools, background knowledge, or time to install the reverse osmosis system, we recommend hiring a local plumber. You can save a lot of money by purchasing the Reverse Osmosis System online, and then hiring a plumber to do the install. Many of our customers go this route.

Four Recommendations When Hiring a Local Plumber to Install Reverse Osmosis System

Reviews Matter

If you don’t already have a plumber whom you know and trust, check out local plumber reviews on the internet. Popular review sites include:

  • Yelp
  • Angie’s List
  • Better Business Bureau
  • Google Reviews can be found by signing into Google and opening Google Maps. Search for “plumber” to see reviews and star ratings for plumbers near you.

Call Around

Once you’ve identified a few reputable plumbers in your area, make phone calls and ask questions.

  • Tell them you have already purchased an RO system and are simply looking to have it installed.
  • Ask if they’re familiar with RO installations.
  • Ask if you can pay them their hourly rate to install a system.
  • Ask how much time a typical RO installation takes.
  • Ask for references.

Still Have Questions about Installing a Reverse Osmosis System?

If you have additional questions, our team of water experts are always happy to answer your query.

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