Does reverse osmosis remove microorganisms?
Bacteria, viruses, and protozoa can exist in water that hasn’t been disinfected – or water that’s been reinfected after disinfection. This can occur due to flooding, cracked pipes, contaminated water heaters and other fixtures, or when water is sourced from untreated lakes and wells.
Most reverse osmosis systems have membranes with almost unimaginably small pore sizes: between 0.001 and 0.0001 microns. This is so small that it approaches the size of water molecules themselves.
The smallest bacteria measures around 0.4 microns, while viruses can measure as small as 0.02 microns. As a result, reverse osmosis systems effectively retain all types of microorganisms.
This means you can technically use a reverse osmosis system to protect drinking water from bacteria like Salmonella and E. coli, viruses like Norovirus, and protozoa like Giardia.
We say “technically” because, all reverse osmosis systems are able to remove these contaminants, they are not disinfection devices.
Reverse osmosis systems don’t destroy microorganisms, only filter them from the water supply. Using a reverse osmosis filter on heavily contaminated water can therefore result in a build-up of bacteria inside the filter housing and on the membrane itself. That’s why standard RO systems are listed for use on “biologically safe water” only.
Does reverse osmosis remove heavy metals? (Lead, arsenic, mercury)
Again, the pore size of all reverse osmosis systems is far smaller than the size of metal molecules, meaning that reverse osmosis systems retain all heavy metals.
Check the specifications of individual systems for the lead removal rating. Most products are rated to remove 95 – 99% of lead and other metals.
Protection against dangerous metals like lead and radon is one of the more common use cases for reverse osmosis filters. It’s relatively easy to install a reverse osmosis system under any faucet used for drinking, to protect the water supply without the need for complex plumbing alterations.
Remember that lead and many other metals have no safe consumption level, meaning that water at risk of heavy metal contamination should always be treated before consuming.