Written by: Gene Fitzgerald // Last Updated:
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So you have decided to add a reverse osmosis water filter system to your home, because you don’t want to be exposed to nasty water contaminants any longer.
You found a great model online and purchased it a couple of days ago. This morning, the system arrived in a big, heavy box. You opened the package to take a first look and…
Wow, you didn’t expect the system to have that many different parts. Hopefully you have the skills to set everything up correctly. After all, you are not a trained plumber. But considering the costs for hiring a professional, it’s a priority for you to do the installation yourself.
Don’t worry, we’ve got you covered! This guide has all the information you need for a trouble-free setup.
How to install a reverse osmosis system:
We have created this reverse osmosis system installation diagram to better illustrate how the individual components are supposed to connect with one another.
This usually single piece of plastic connects the RO system components. This includes the pre and post-filters, the RO faucet, and the storage tank. Some units will come with a bracket to mount the system module.
Pre-filters are usually a sediment pre-filter for debris (there may be more than one depending on your system and feed water needs) and a carbon filter for chlorine and chemicals.
Both help to protect the delicate RO membrane from damage and fouling – before the unfiltered water gets to the reverse osmosis membrane, it will pass through the sediment and carbon pre-filters.
The RO membrane is the main water filtration component and is what will eliminate most of your contaminants after they have passed through the pre-filters.
RO-filtered water will leave the storage tank and pass through the post-filtration stages. These may vary depending on your unit but can include a remineralization filter, and a carbon filter to eliminate any strange tastes or smells from the storage tank.
This pressurized tank stores the RO water after it has passed through the RO membrane, and it ensures you always have filtered water on demand.
This faucet is separate from your main spout, and it means you do not have to waste your RO water on things like dishwashing and can use your main faucet for that.
The drain saddle and line direct the wastewater produced during filtration away from the unit for disposal.
This valve is the connecting valve between your RO system and the water supply under your sink.
The auto shut-off valve will stop the system from filtering water when the storage tank reaches capacity, and it will switch on again once the water in the tank is used.
This valve prevents water from flowing back towards the RO membrane possibly causing damage.
This increases the pressure of the water passing through the RO membrane, and restricts wastewater production.
Various tubes and lines connect the different components of the RO system.
RO systems usually use easy-to-connect, color-coded quick fittings, so you know what goes where.
Installing under the kitchen sink is the standard, albeit not always the most convenient solution due to limited space. Other options are the basement, garage or a utility room, running a water line to the kitchen sink (delivery pump may be required).
What’s important is that you install on a cold water line, downstream of any other water treatment equipment such as a softening system. Also, do not install where freezing temperatures may occur.
Do you have an extra hole in your sink? You’ll need to drill one if there’s none. Use a flat surface where you can use the faucet conveniently without disrupting other kitchen tasks like doing the dishes.
The water storage tank needs to be within 10 ft of the reverse osmosis faucet if you don’t want to experience low-pressure issues. A tank can stand upside or lay on its side.
This saddle needs to be connected to your sink’s drain pipe. It’ll fit a standard-sized pipe of one-and-a-half inches. Go above the P/J-trap and far away from any disposal. Both vertical and horizontal pipe sections work, although horizontal is recommended for noise reduction.
It’s time for you to learn how you can hook up your new reverse osmosis under sink system. With a little bit of preparation and the necessary tools it’s really not that difficult to pull off.
Also, every system should come with detailed installation instructions. If that isn’t enough, you can find plenty of helpful videos on YouTube.
And lastly, individual steps may vary from product to product and also depend on your specific plumbing setup. Therefore, the following instructions are given as a general guideline. Remember: All plumbing must be completed in accordance with state and local codes.
It might already be too late, but prior to purchasing a reverse osmosis system you should ensure that there is enough space under your kitchen sink to accommodate a filter module + tank.
Furthermore, you need to make sure that there actually is a cold water line that you can use as your feed source (which, of course, is nearly always the case).
Once the system has been delivered, unbox it and double check that all components fit in their desired location. This way you know if you need to make adjustments to pipes etc. before you can start with the installation itself.
Gather all the necessary tools and components beforehand. Having everything lined up can save you from a lot of frustration. The following list makes no claim for completeness:
Let’s start by installing the reverse osmosis faucet that will soon provide you with clean, great tasting drinking water.
Again, you need to decide where you want to place it – unless your sink already has an extra hole that you want to use (might be covered by a chrome plate). If not, you have to drill a new hole in the sink or countertop. The faucet should be positioned with convenience in mind. A flat area is required.
Please note: You may require a special type of drill bit to prevent scratching or chipping depending on the material.
For a stainless steel sink, mark the spot with a center punch. Then gently grind away enough surface material to safely accommodate the ¼” drill bit. Now carefully drill a hole. Go extra slow (a drop of oil can work wonders). For a ⅜” or ½” hole, drill a ¼”pilot hole first.
When you are done, remove any remaining metal chips that could damage the surface and clean up sharp edges.
Put the faucet stem through the hole and secure it from the bottom with washers and a hex nut. Then attach the quick connect fitting and tighten with a wrench.
Congratulations, you have just completed the hardest task!
The next step is to install the drain saddle a.k.a. drain line adapter on the drain line.
The saddle/adapter should be placed above and as far away as possible from the dishwasher discharge and garbage disposal to avoid clogging and to protect your RO system from potential contamination and fouling. What’s more, it should be at least 6″ above the p-trap.
Drill a ¼” hole in the top or the side of the drain line (never the bottom). Secure the drain clamps with bolts aligning the clamp hole with the hole in the pipe. Be careful not to overtighten.
In step three, we are going to install the inlet feed valve which connects your reverse osmosis system to the cold water line.
First, turn off both the cold and hot water supply. If valves are inoperable, shut off the entire water to your home. Then release the pressure in the water lines by opening respective outlets. Remove the tubing from the cold water valve. Install the new feed valve (adapter might be required) and tighten with a wrench. Make sure to close the feed valve for now.
Connect the cold water tubing to the new valve (adapter might be required) and turn the water supply back on.
You want to place the water storage tank within 10 feet of the drinking water faucet in order to not lose significant pressure. (Keep in mind that, depending on its size, the tank can weigh more than 25 pounds when filled to the top.)
Before putting it in position, wrap about 6 layers of Teflon tape around the threaded port at the top. Then screw on the tank valve or tank connector. They should thread on easily and only need to be hand-tight.
By the way, with many systems the storage tank can also be placed on its side without compromising filtration performance. This comes in handy if you don’t have much space in your kitchen cabinet.
When mounting the RO module, which is optional, take into consideration that every once in a while you will need to replace the RO membrane + filters and possibly perform other maintenance tasks. In other words, there needs to be sufficient space underneath the system.
To connect the module we use the color-coded tubing. Most systems come with quick-connect fittings. Simply push the tubes into their respective fittings as far as they will go. You can test a connection by trying to pull back gently.
FYI: Water residues in the tubing means that the system was tested by the manufacturer. Keep a towel at the ready!
Pro tip: Trimmed connections will maximize water flow. At the same time, extra tubing might come in handy if the system ever needs to be relocated.
Insert the various pre-filters and the RO membrane into their housings according to the instructions provided:
Usually, the first filter is a sediment pre-filter, followed by carbons pre-filter(s), and lastly the membrane. Then come the post-filters.
Finally, it’s time to start your new reverse osmosis system. Here is how:
Some manufacturers recommended to flush a new system 2-3 times before use. Once you’ve done that the setup is complete and your water is ready for drinking.
A video says more than a thousand words!
An under sink RO system may be connected to an ice maker, fridge, or coffee machine. To do this, an extra pump may need to be installed to make sure you have enough pressure in the water lines for it to reach these appliances.
Countertop units will not be able to be connected to these things.
Not everyone feels comfortable installing an RO system DIY-style. If you, too, prefer to turn to an expert we recommend you simply contact a local plumber in your area.
How much the installation will cost depends first and foremost on the type of system you want to have installed:
If you don’t already have a plumber in mind whom you trust, checking out local reviews online is a great starting point. Some popular sites you can use are:
Asking for estimates from more than one plumber will likely save you a lot of cash. Let them know that you have already purchased a system, but need help with the setup. Ask for their expertise and references.
By installing a reverse osmosis water filtration system, you can enjoy benefits such as:
If you have any questions or thoughts about installing a reverse osmosis system please don’t hesitate to leave a comment below!