Reverse Osmosis (RO) filters are highly capable water treatment systems. With technology originally developed to desalinate seawater, RO home systems pack a serious punch, filtering your mains supply down to the size of individual molecules and ions. This makes reverse osmosis a common choice for those looking to ensure water safety—either from potential viruses and bacteria in private well systems, or the heavy metals that can remain in old pipes and plumbing.

Whatever your need for advanced home-filtering, we’ve put together a list of the best reverse osmosis systems you can buy today. Scroll down for the details.

In a rush? Key points:

  • Reverse osmosis systems will improve some aspects of water’s taste and smell, but they’re really designed to ensure water safety.

  • Reverse osmosis filters will go above and beyond standard carbon filtration, dealing with viruses, bacteria, metals, and other nasty contaminants.

  • Reverse osmosis filters are mostly found in whole-house systems, installed at the point of entry (POE) where the water main enters your home…

  • …Though, there are some under-sink and countertop models on the market that use reverse osmosis.

  • All reverse osmosis systems are relatively slow-filtering, meaning that high usage over a short period can lead to water shortages.

  • Most pair their reverse osmosis filters with an activated carbon stage, to remove the smallest molecules left behind by RO.

  • There’s an argument for reverse osmosis being the highest-grade filter mechanism available to buy for individual homes.

What is reverse osmosis?

Osmosis is the natural migration of water across any semi-permeable membrane. Left to its own devices, water will always move across a membrane in the direction of the space with the most dissolved solutes, seeking out the highest concentrations of particulates or contaminants in order to create an equal distribution across the whole body of liquid.

Reverse osmosis takes this water flow gradient and reverses it, applying an external force to make water travel across a series of semi-permeable membranes from a more concentrated to less concentrated solution.

These membranes are so fine that they can effectively remove contaminants almost down to the size of water molecules themselves (0.0005 microns in some systems!) Usually, an RO filter will employ three to five membranes, descending in filtering size, with the first designed to take out large particles of sediment, while the final membrane targets viruses and bacteria.

All of this gives RO filters the power to remove common waterborne and disease-causing protozoa, such as cryptosporidium and giardia. They’ll also easily rid your H2O of bacteria like E. coli, and take care of viruses such as the norovirus. As confirmed by the CDC, an NSF-certified RO filter will also deal with harmful metals like chromium and lead, which can leak into your water supply from old pipes and degrading fittings.

For those who need to go deeper into the how’s and why’s of reverse osmosis, here’s our extended look at Everything you need to know about reverse osmosis filters.

FAQs

A good quality RO filter removes so many pollutants and contaminants from water, it’s easier to talk about what they don’t filter out. Because reverse osmosis relies on membranes small enough to let water molecules through (catching anything bigger) anything smaller or equal in size to water itself may also make it past the filter.

Contaminants of this size include organic compounds and dissolved pesticides, herbicides, solvents, hydrogen sulfide, chlorine, and radon. Luckily inexpensive activated carbon filters are able to readily adsorb organic contaminants such as these, hence why you’ll almost always find an RO filter paired with a carbon module.

Aside from those compounds, however, you can feel confident that reverse osmosis will take care of almost all larget compounds (As long as the system is effectively maintained) These include:

  • Fluoride
  • Asbestos
  • Algae
  • Bacteria
  • Protozoa
  • Lead
  • Arsenic
  • Mineral rocks and metals
  • Sediment and rust

Note: always check individual filter specifications for an exact list of filterable contaminants.

Running water through an RO filter should noticeably change the taste of water. Removing sediment and minerals will result in softer, purer water, which some may prefer (and others may actually find odd at first).

Many of the organic compounds with a similar molecular size to water are unfortunately the same contaminants responsible for those nasty tastes and smells in your tap supply. Chlorine—a byproduct of treatment-works—gives off that familiar swimming-pool odor, while hydrogen sulfide and other gasses are responsible for the foul-smelling egg, fishy, or musty aromas. Lovely.

As said above, however, it’s easy and common to add a carbon filtration stage to your set up, effectively dealing with these leftover pollutants.

The best thing to look for when shopping for RO filters is an NSF Standard 58 certification. This badge of quality confirms that claims made by filter manufacturers are backed-up by testing. 

Specifically, Standard 58 says that a filter will always remove Total Dissolved Solids (TDS), and will remove bacteria, viruses, metals, and all of the contaminants listed above if the manufacturer claims so.

There is some discussion on the internet as to whether water from RO filters presents a health risk over the long term. It’s not completely clear where these claims originate from, as the reverse osmosis process doesn’t add anything (no chemicals, electrical charge, salts, etc.) to the water source.

One source of these health worries may stem from improperly maintained filter membranes. Because RO membranes collect bacteria and impurities from water on a daily basis, these contaminants can build over time, coating the membrane surface to the point where a replacement is needed. If membranes are not replaced according to recommendations—or if they are not fitted properly—bacteria can be dislodged to other parts of the filter, where it can multiply and re-contaminate water.

Another possible reason for discussions over the safety reverse osmosis may stem from the power of the filter. RO systems are so good and removing anything non-H2O from your mains supply, that traditionally desirable minerals such as calcium, magnesium, and zinc (not to mention fluoride) will also be caught by RO membrane stages.

While this is neither a necessarily good or bad thing, many will value the micro-minerals that water can supply on a daily basis—for their taste as well as nutritional value. Furthermore, there are some scientific indications that high-mineral content tap water has been associated with lower incidences of cardiovascular disease in general populations.