How to Build Your Own DIY Reverse Osmosis Water Filter System

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Compared to other types of water filters, reverse osmosis systems are quite complex, but that doesn’t mean they can’t be fully or partially assembled at home.

Now while you can’t build an RO system out of duct tape and coffee filters, as long as you source the required parts from a reputed supplier you can put together your own unit.

You will need a specific set of components – but as long as you have some DIY and plumbing know-how, making a reverse osmosis system should be a doable project.

Want to learn more? Continue reading!

Key Takeaways

  • Reverse osmosis systems are quite complex in a sense that building one from scratch would be extremely difficult if not impossible and not save you any money over purchasing a pre-made unit.
  • One alternative is buying all the ready-made components separately and then installing them yourself. This is as close as you’ll get to making your own DIY RO system at home.

Is It Hard to Make a Reverse Osmosis Water Filter System Yourself?

First of all, you cannot build a reverse osmosis system using your own components. For one, the manufacturing process required for producing RO membranes is highly complex and not something for a DIY project.

That said, assembling a reverse osmosis system using ready-made components is not that hard of a job, but it does require some planning and skill. Essentially, you’ll need to purchase all of the necessary components and then make sure they fit together and function correctly.

Side note: You won’t save a significant amount of money by building your own RO system this way, but if you have your heart set on building your own, then continue on for detailed instructions.

The system will require an RO membrane and housing, carbon and sediment pre-filters with housings, a flow restrictor, ASO valve, a storage tank, plus tubing and fittings.

Buying a Filter System and Connecting It Yourself

A practical alternative to building a reverse osmosis system from scratch is purchasing a basic pre-assembled unit and then connecting it yourself – not the most genuine DIY project but at least it will save you on installation costs.

plumber installing reverse osmosis system under sink

Homemade RO System Components

Every RO system will require the following parts for installation and assembly. Depending on the type of installation you’re going for, these parts may come bundled with a pre-assembled system, or they may need to be sourced separately.

Feed Water Valve

The feed water valve is the valve that connects the RO system to your sink’s cold water supply. It allows unfiltered water to flow into the system.

Tees

Tees are T-shaped fittings with three quick connections on them. These are used at several points in the RO system, including for running filtered water from the RO membrane to the storage tank and/or the post-filter. The three-way design allows the water pressure to dictate which directions the water flows.

Elbows

Elbows are small 90-degree-shaped connectors used for connecting piping to an outlet at a perpendicular angle. This is useful for making clean connections that won’t leak or take up excessive space.

Pre-Filters (Inline)

RO systems require pre-filtration to protect the sensitive membrane from clogging or fouling. RO membranes are especially sensitive to sediment/silt as well as chlorine – which is why these contaminants must be removed during pre-filtration.

A reverse osmosis system will typically feature both a sediment pre-filter to capture silt, sand, rust, and other large particles, as well as an activated carbon pre-filter to remove chlorine and other chemicals.

RO Membrane + Housing

The RO membrane is the workhorse of any RO system and uses ultra-fine mesh to separate a wide array of contaminants from water. The membrane sits inside a housing, which keeps it protected and allows for easy connectivity with the rest of the filtration system.

Automatic Shutoff Valve

The automatic shutoff valve (ASO) is another key component used for regulating the filter operation. When the storage tank has filled to a pre-set level, its internal pressure triggers the ASO valve to shut off the filtration process.

Check Valve

The check valve is used to stop the flow of water backward from the storage tank into the membrane housing. This is vital for preventing damage or rupture of the sensitive RO membrane, as backward flow can destroy it.

Flow Restrictor

The flow restrictor is used to slow down the flow of waste water out of the system. This keeps the pressure inside the RO membrane in the optimal range and prevents the excessive creation of waste.

RO Storage Tank + Tank Valve

As reverse osmosis filtration is a slow process, a storage tank is needed to keep a reserve of filtered water on hand for immediate use. The storage tank is pressurized to avoid the need for a pump and will fill itself automatically until it triggers the ASO to shut off the filtration process.

The tank valve sits on top of the storage tank and allows you to shut off the water supply to the tank manually. This is needed for cleaning/sanitizing or repressurizing the tank.

Tubing

Food grade tubing – usually ¼” – is used for transporting water from the feed water valve, through the pre-filters, membrane, post-filter, and onto the RO faucet. This tubing is often designed to work with quick-connect fittings, so setup is simple and fast.

Drain Saddle

The drain saddle is where the RO system connects to the drain pipe under your sink. It requires drilling a hole in the drain pipe to install.

Mounting Clips

Mounting clips are used for attaching the RO membrane and pre and post-filters to the membrane housing.

Water Dispenser

The RO faucet dispenses filtered water at the kitchen sink. Under sink style RO systems use a separate faucet from your main kitchen faucet, so they require a faucet installation somewhere on your sink or countertop.

young girl opening reverse osmosis faucet

DIY Reverse Osmosis – How to Build Your Own RO System at Home from Preconfigured Components

If a DIY reverse osmosis setup is what you’re after, then the process outlined below should give a clear idea of the installation process.

Tools You’ll Need

  • Tube cutter or sharp utility knife
  • Adjustable wrench or filter wrench
  • Plumber’s tape

How to Install

Step 1: Apply Plumbers Tape to Fittings

Plumber’s tape is thin Teflon tape used to make fittings watertight and easier to thread. Wrap tape 2 or 3 times around any threaded connections you need to make while assembling the system.

Step 2: Install Membrane Housing Fittings

First, insert the check valve into the membrane housing. If you aren’t sure which outlet the check valve is supposed to connect to, check the manufacturer’s instructions. Next, insert an elbow fitting into the other outlet on the membrane housing for the drain connection. Then, insert another elbow fitting into the other end of the membrane housing for the feed water inlet.

Step 3: Install Membrane in Housing

Now, open the RO membrane packaging and slide it into the membrane housing. Make sure the side with the two O-rings slides in first. RO membranes are sensitive, so to avoid damaging, wear rubber gloves or use the plastic packaging to handle the membrane.

Then screw on the housing’s end cap and make sure the O-ring is sealed correctly.

Step 4: Set Up the Pre-filters

Assuming your system has both a sediment pre-filter and a carbon pre-filter, you’ll need to repeat the same process for both.

First, attach a length of tubing to the outlet on the pre-filter. The pre-filter housing should have a directional arrow on it, so you’ll know which side is the inlet and outlet.

For the second pre-filter (typically activated carbon), cut down the tubing to a manageable length and attach the free end to the automatic shutoff valve. For the first pre-filter (typically the sediment filter), the tube will connect to the inlet on the second pre-filter.

Step 5: Attach ASO Outlet to Membrane Inlet

Next, attach another length of tubing to the outlet on the ASO and cut it down to size. Then attach the free end to the inlet on the membrane housing.

Step 6: Attach the Check Valve to the ASO

Next, insert a length of tubing into the check valve outlet on the membrane housing. Then, cut this down to size and insert the free end into either of the remaining connectors on the ASO.

Step 7: Attach the ASO to Tee

Now, attach the final remaining connector on the ASO to your Tee fitting. The T-fitting has three connectors on it, one running to the ASO, while the other two run to the storage tank and post-filter.

Step 8: Attach the Tee to the Post-Filter

Next, run a length of tubing from the free connection on top of the Tee to the post-filter. The bottom of the T-fitting will run to your storage tank.

Step 9: Clip the Filters to the Membrane

To secure the system, you’ll need to attach the pre and post-filters to the membrane housing using mounting clips. This will make the whole system easy to maneuver and manage.

blue reverse osmosis membrane

Step 10: Set Up Drain Line

Next, attach another length of tubing to the last remaining elbow fitting on the membrane housing. This is the drain line that will run the waste water down your drain, so its other end will need to be mounted to your sink’s drain pipe using a drain saddle.

Step 11: Attach Faucet Line to RO Faucet

The outlet line running from your post-filter will need to be connected to the RO faucet on the countertop. Installing the RO faucet is another task that will need completing, but if you’re lucky, you’ll be able to install it in a spare hole for the sprayer or soap dispenser.

At this point, the filter setup is essentially complete. All that remains is connecting the storage tank to the Tee fitting, connecting the first pre-filter to the feed water valve, and installing the RO faucet on the countertop. These steps can differ depending on your setup and system, so be sure to follow the manufacturer’s instructions.

What Is a Homemade Reverse Osmosis System?

A homemade reverse osmosis system is not exactly what it sounds like at first. The system is more of a semi-DIY assembly and installation than building an RO system from scratch.

Going this route can save you some costs on parts and certainly on installation, so it may be worth considering if you’re handy with tools and DIY.

Benefits of RO Water Purification

Whether you go with a DIY system or a pre-assembled one, the benefits of reverse osmosis water purification will be the same:

  • Effective contaminant removal: Reverse osmosis is a highly effective filtration method and as such it removes a wide array of water contaminants. It will reduce or eliminate chlorine/chloramine, sediment, nitrites/nitrates, pesticides, VOCs, heavy metals, and most microbial contaminants among other stuff.
  • Taste and smell: As RO removes nearly everything from water except pure H2O, you’re left with incredibly neutral and smooth-tasting water.
  • Filtered water on demand: RO systems use a storage tank to keep enough filtered water on tap for your needs. This makes them easier to use than systems requiring manual re-filling.
  • Save money: If you compare the cost of RO water to bottled water, you’ll quickly notice significant savings even during the first year.
  • Easy to install and maintain: Most RO systems are fairly easy to install and maintain. All that’s needed as far as maintenance is regular filter changes and periodic cleaning/sanitizing of the system.
  • Customizable: RO systems, especially DIY setups, are highly customizable. You can add on additional filter stages like UV filters or remineralization stages, install a permeate pump, etc.

If you have any questions about homemade reverse osmosis please don’t hesitate to leave a comment below!

About the Author Gene Fitzgerald

Gene Fitzgerald is one of the founders of BOS and currently head of content creation. She has 8+ years of experience as a water treatment specialist under her belt making her our senior scientist. Outside of BOS, Gene loves reading books on philosophy & social issues, making music, and hiking.
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