Reverse Osmosis Waste Water Disposal Guide

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Reverse osmosis water treatment comes with a known downside: It wastes water.

But how do you dispose of reverse osmosis waste water?

This guide is all about reverse osmosis waste water disposal, and how you can reuse yours to minimize waste.

Key Takeaways

  • Most of the time, you don’t have to worry about disposing of your reverse osmosis waste water. RO waste water is flushed out of the system and goes down the drain automatically.
  • Under sink and whole house RO systems usually have a direct drain connection.
  • Countertop RO systems can be different. They often have a separate tank that stores waste water temporarily. The tank is emptied manually from time to time.

How to Dispose of Reverse Osmosis Waste Water?

During reverse osmosis purification, water diffuses through the semipermeable RO membrane. Any impurities are rejected. But not all of the water makes it through the membrane either.

The result: The feed water is split into 2 streams; the permeate (purified) water and the reject (contaminated) water. The filtered water is often stored in a tank for later use. The waste water is simply disposed down the drain.

plumber installing reverse osmosis system under sink

Your drain connection differs depending on the kind of reverse osmosis system you have.

  • For example, most under sink RO systems have a direct drain connection. This means that there’s a waste water tube from the RO membrane to the sink’s drain pipe. This waste water tube is connected to the drain saddle, which is installed on the drain pipe. The drain saddle is basically a hole in the drain pipe where you insert the drain tube. The result of this connection is that waste water from an under sink RO system goes down the drain directly.
  • Countertop units are quite different. A lot of them have no connections to the plumbing system, so they store waste water in a separate tank that needs to be emptied manually every now and then. Notwithstanding, some countertop systems have a loose drain tube that you can route into any type of drain or container.
  • As for whole house reverse osmosis systems, they always have a direct drain connection. This is because they use a lot more water than the other system types and also produce a lot more waste. There’s no realistic way to store all that waste water, so everything is set to go directly down the drain.

In essence, you don’t really have to worry about reverse osmosis waste water disposal most of the time.

Besides, although RO waste water contains more contaminants, it’s not a corrosive mixture.

How to Use Reverse Osmosis Water Instead of Disposing It

Letting any water go to waste can feel rather uncomfortable, especially considering the state of the Earth today. Reverse osmosis might waste water, but there are safe ways to reuse that water to prevent it from completely going to waste. We’ve discussed some of these ways below:

Cleaning Routines

RO waste water can easily be used to handle your everyday cleaning routines. You can use waste water for mopping floors, doing dishes, cleaning bathrooms and kitchens, cleaning windows, and washing driveways or patio decks. These tasks don’t require purified water, so waste water takes care of them perfectly. Simply add some soap to the water, and it’s ready for use!

Laundry Pre-Rinse

Using RO waste water for your laundry pre-rinse is a great way to save it. Waste water contains filtered salts that can help remove tough stains in clothes before the main wash.

But remember, you’d have to be careful using waste water on delicate clothing. If your waste water has high TDS levels (which is very likely), your soft and delicate clothing could get damaged. So if you’re pre-rinsing with RO waste water, leave out your delicate fabrics.


RO waste water can be great for irrigation since it contains minerals and nutrients that plants need. Just be careful about elevated salt levels.

Washing Your Car

Car washing consumes a lot of water (sometime as much as 65 to 80 gallons), and since your car doesn’t demand filtered water, there’s no reason to waste it. RO waste water is the perfect alternative and allows you to save your precious tap water for more important tasks, like cooking.

Why Does RO Waste Water in the First Place?

As mentioned, reverse osmosis systems filter water by forcing it through a semipermeable membrane under high pressure. The RO membrane has really tiny pores that contaminants can’t pass through.

As filtration progresses, a lot of contaminants are trapped on the membrane. If left unchecked, these contaminants can accumulate and clog the membrane. To stop this from happening, the RO system uses some of the feed water to flush the membrane. The combination of the contaminants and the water used to clean the membrane is the waste water, and all of it is flushed down the drain.

Flushing the membrane and wasting water in the process is the only way to prevent the membrane from getting clogged and failing prematurely.

blue reverse osmosis membrane

How to Lower the Amount of Waste Water Being Produced

There are simple things to do to bring your reverse osmosis waste water production to a minimum:

Water Pressure

Your feed water pressure plays the most significant role in determining how much waste water your system produces. The ideal water pressure for RO systems to thrive is 60 psi. Anything lower than this causes your system to produce more waste. If your system’s pressure doesn’t measure up, there are ways to increase it. They include:

  • Adding a booster pump to the system.
  • Adding more pressure to your home’s plumbing.
  • Increasing water pressure at the pressure valves (in systems that have one).

Permeate Pump

Permeate pumps can reduce waste water production, too. But unlike booster pumps, they reduce waste water levels by 75-80% without using electricity.

Permeate pumps use the waste water to power a piston which forces filtered water into the storage tank. This stops the pressure in the tank from pushing against the membrane and increases the system’s efficiency.

Filter Replacements

Replacing your filters when due is non-negotiable in your quest to minimize your waste water production.

You’d have to replace your pre and post-filters and RO membrane at the right time. Most filters and membranes are to be replaced every 6-12 months and every 2-5 years, respectively. There’s no universal time frame for replacing filter elements though, so check your manufacturer’s instructions to note when your filters need to be replaced.

Continuing with an old pre-filter or RO membrane after it has outlived its usefulness is a recipe for excessive waste water production and even contaminated “filtered” water.


A better option to sending your waste water down the drain is recirculating it through the RO system to be repurified into clean water. Doing this means your waste water never completely goes to waste. So instead of sending your waste water down the drain, recirculate it to give it a chance to become purified water.

Using Evaporators to Dewater RO Reject Water

Using evaporators to dewater RO reject or waste water only applies to filtration in industrial settings. A lot of waste water is produced during these industrial processes, and where to dispose of this waste water can be tricky.

To bypass this problem, RO reject or waste water is “dewatered” or vaporized. This means the water molecules are all taken out, leaving behind contaminants that are much easier to dispose of.

Special evaporators are used to carry out this operation.

If you have any questions about reverse osmosis waste water disposal 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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