Does Reverse Osmosis Remove All Contaminants (Everything)?
Written by: Alexandra Uta // Last Updated: Mar 31, 2023
This page may contain affiliate links. If you buy a product or service through such a link we earn a commission at no extra cost to you. Learn more.
Flaunted as one of the most effective water filters on the market, reverse osmosis systems have gained an excellent reputation, and for a good reason.
Their multi-layered membranes prevent water impurities and pollutants from reaching your faucet at a very high rate.
But can reverse osmosis remove everything from water? Read on to find out!
Contents
show
Key Takeaways
- Reverse osmosis removes the vast majority of contaminants from water but not all.
- Reverse osmosis removes sediments, pesticides, VOCs, microorganisms, and ions including aluminum, ammonium, arsenic, barium, cadmium, calcium, chloride, chromium 6, copper, cyanide, fluoride, iron, lead, manganese, magnesium, mercury, nickel, nitrates, phosphate, potassium, radium, selenium, sodium, sulfate, sulfite, and zinc.
- Some compounds like atrazine and benzene may pass through an RO membrane. The same goes for dissolved gasses like chlorine and carbon dioxide. That’s why RO systems use additional pre and post-treatment.
Does Reverse Osmosis Remove All Contaminants?
So, does reverse osmosis remove all contaminants from water? Unfortunately, no,
A water filter that removes all contaminants still hasn’t been designed. However, reverse osmosis is as close to perfection as a water filter can get.
Thanks to the semipermeable RO membrane, which can trap as tiny impurities as .0001 microns in size, reverse osmosis is capable of removing all major tap/well water contaminants and more.
A well-maintained reverse osmosis membrane will get rid of sediments and other dirt, harmful pesticides, asbestos, volatile organic compounds, pharmaceutical residue, bacteria, viruses, cysts, and other microorganisms. It can also reject up to:
- 98% of aluminum and ammonium
- 97% of copper, mercury, nickel, sulfate, sulfite, and zinc
- 96% of arsenic, barium, cadmium, calcium, iron, lead, manganese, and magnesium
- 95% of selenium
- 94% of chromium 6
- 90% of potassium and sodium
- 88% of chloride, cyanide, and fluoride
- 80% of radium
- 68% of nitrates
In addition to these, a reverse osmosis membrane can also reduce the turbidity in water by 97.5%.
Keep in mind that this is the RO membrane alone. A full-blown reverse osmosis system that includes pre and post-filters offers additional protection and can trap even more contaminants.
Does Reverse Osmosis Remove Everything?
Reverse osmosis does not remove everything found floating around in our water supplies these days.
A reverse osmosis membrane usually has a salt rejection rate of 95 to 99%, which means that the dirtier the feed water, the more contaminants will end up in the permeate water. If you have cleaner input water to begin with, there will be less impurities in the RO water.
Reverse Osmosis and Healthy Minerals
An RO membrane is not a smart membrane. It cannot possibly differentiate good from bad. So yes, a reverse osmosis membrane will try to remove everything it can detect in your water, including good minerals like calcium or magnesium.
So truth is, RO-purified water is mineral deficient. How come that’s good for your health?
For one, a well-balanced diet can provide you with the needed daily intake of minerals. Less than 5% usually comes from our drinking water.
Plus, don’t forget about all the dirt that a reverse osmosis system removes. It would be much healthier to drink water without calcium and lead, than consuming water that’s rich in minerals but also contains toxic heavy metals.
So if you’re wondering whether getting an RO system is worth it, that should seal the deal.
Further Reading:
What’s Not Removed By Reverse Osmosis
Reverse osmosis can remove most water contaminants, but some tiny particles may get through. Those include:
- Some pesticides, including atrazine
- Some organic compounds, including benzene
- Dissolved gasses cannot be removed at a high rate. Carbon dioxide, chlorine, and radon are not heavy enough or ionized, and they can get through unless additional filtering is in place.
But don’t despair! What’s not removed by the RO membrane will most likely be rejected with the help of additional filters.
Carbon filters are unrivaled when it comes to providing additional filtering support. They are used both as a pre-filter and post-filter (polishing filter), and they can remove chlorine, hydrogen sulfide, disinfection byproducts, etc. Plus, they will seriously improve the taste and odor of the water.
Test Your Water!
Before committing to any water treatment, it is wise to have your water quality tested to know what you’re dealing with and what measures should be taken.
And this doesn’t always have to be costly, high-end laboratory testing. There are many affordable water testing strips you can choose from. They are usually one-time tests designed to read which contaminants (and in what concentration) are present in your water supply.
This is a highly recommended step that can indicate the need for pre and/or post-filters.
What Is a Reverse Osmosis System and How Does It Work?
A reverse osmosis system is a multi-stage filtration method that doesn’t solely rely on the RO membrane’s filtration but includes additional filters, too.
In a reverse osmosis system, there are at least four stages:
- First, the water from the supply gets in touch with a sediment pre-filter. This filter is in charge of removing larger particles. This is an essential part of the system, as pre-filtering also prolongs the lifespan of the RO membrane.
- Next comes a carbon pre-filter which removes chlorine and other chemicals.
- Then, the pre-filtered water (with less chlorine now) moves to the RO membrane. The semi-permeable membrane traps tiny impurities and allows clean water to move to the next stage.
- Finally, the purified water goes through a post-filter (usually carbon) for further purification and taste improvement. Filtered this way, the water is clean, odorless, and safe to drink.
RO systems may also include remineralization cartridges, UV disinfection, pressure pumps, etc. Each additional filter/element takes the filtration of the system to a higher level.
If you have any thoughts about the question, does reverse osmosis remove all contaminants, please don’t hesitate to leave a comment below!
About the Author Alexandra Uta
Information provided on BOS is for educational purposes only. The products and services we review may not be right for your individual circumstances.
We adhere to strict editorial guidelines. Rest assured, the opinions expressed have not been provided, reviewed, or otherwise endorsed by our partners – they are unbiased, independent, and the author’s alone. Our licensed experts fact-check all content for accuracy. It is accurate as of the date posted and to the best of our knowledge.