Does a Reverse Osmosis System Need a Drain? Find Out Here!

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In the world of water filters, there are many different kinds.

Many water filtration methods work by trapping contaminants and holding them, such as carbon filtration, or inactivating pathogens in the water so that they are no longer dangerous, such as UV purification.

But reverse osmosis works a little differently, and most RO systems come with a drain line. Why is this needed? And do all reverse osmosis systems needs a drain? Let’s find out.

Key Takeaways

  • Most reverse osmosis systems will need a drain to remove the wastewater from the unit, ensuring the RO membrane stays intact.
  • Some RO system models do not use a drain line but a wastewater tank, and some will have modified drain lines leading to the hot water lines or something similar.

Does a Reverse Osmosis System Need a Drain?

In most cases, yes, a reverse osmosis system needs a drain. That’s because the water contaminants rejected by a reverse osmosis membrane need to be washed away. Otherwise, the membrane would clog in no time.

In other words, reverse osmosis water filtration produces contaminant-laden wastewater which needs to go somewhere!

Do All Reverse Osmosis Systems Need a Drain?

The exception to the rule is usually a countertop reverse osmosis system model. These often come with a tank that collects the wastewater, which needs to be emptied manually – into a drain!

Some RO systems will also be designed to reroute the wastewater to use it for other purposes, for example, into the hot water lines for washing dishes or they reroute it back to the RO membrane.

Why Does an RO System Need a Drain?

A reverse osmosis filtration system needs a drain to carry away the impurities you want out of your water, and not having a drain to take the wastewater defeats that purpose.

Unlike some other forms of water filtration, reverse osmosis filters impurities, but it does not hold the contaminants, and they need to be rinsed away to make sure the RO membrane does not foul or damage prematurely.

plumber installing reverse osmosis system under sink

Reverse Osmosis System Drain Requirements

While each model and system will vary a little, you can expect the following from a standard under sink reverse osmosis system:

  1. The wastewater exits the membrane housing through the check valve.
  2. The wastewater passes through a flow restrictor.
  3. Wastewater enters the main drain pipes through an attachment called a drain saddle.

Connection Point

A reverse osmosis system is usually installed under the kitchen sink so that the RO drain line can be easily connected to the sink’s drain pipe.

To connect the RO drain line to the drain pipe in the kitchen, you need to drill a hole in the drain line and attach the drain saddle.

Drain Line Size

A reverse osmosis drain line is usually ¼ of an inch to ⅜ of an inch in diameter. If you are planning to have your system in a different area, or you are planning to run your waste water to another part of the house, then you may have to replace the drain lines that come with the system with longer ones with the same diameter.

Proximity of Drain to RO System

An RO drain line does not require a whole lot of pressure to push the water through, so you can run them pretty far away from the system itself. For example, if you want your wastewater flowing into a wastewater tank outside for gardening or car washing, you probably can do so.

How Reverse Osmosis Drain Systems Work

Several components of a reverse osmosis drain system keep it functioning effectively and keep contaminants away from your clean water.

Flow Restrictor

A flow restrictor does exactly what the name suggests. It controls the amount/speed of water that goes down the RO wastewater drain. Without a flow restrictor, way too much water would flow down the drain instead of through the RO membrane.

Flow restrictors will vary in size depending on your RO system’s production/filtration rate. For example, a system that filters 50 gallons of water per day will need a larger flow restrictor than one that filters 25 gallons per day.

Drain Saddle

This is the device that attaches the reverse osmosis drain line to your under sink drain pipe. It can be installed by drilling a hole into said drain pipe and bolting the drain saddle to the pipe.

If you have any thoughts about the question, does a reverse osmosis system need a drain, please don’t hesitate to leave a comment below!

About the Author Alexandra Uta

Alex is a content writer with an affinity for research and a methodical attention to detail. Since 2020, she has fully immersed herself into the home water treatment industry only to become an expert herself. Alex has been using water filters and similar products for years which has gained her lots of hands-on experience.
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