Best Reverse Osmosis Systems

Now, while Reverse Osmosis may sound like the name of a trendy rock band, it’s really one of the best ways to produce clean water for your home. 

As opposed to other water filters, the reverse osmosis (RO) systems are very efficient, often capable of removing up to 99% of harmful contaminants that float in regular municipal or well water.  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.

Reverse osmosis systems target specific dissolved inorganics like fluoride, lead, and arsenic and are great at removing the metal-like taste and odor from municipal well water.

Reverse Osmosis systems are also great at removing chlorine from your water as well. So, if you’re worried about contaminants, taste, and/or odor, then reverse osmosis systems are one of the most powerful filtration systems on the water filter market as they remove a wider range of contaminants than most alternative systems.

Before making your RO choice, there are a few things to consider, specifically the water that comes into your house and its feed system. City or municipally treated water will be relatively free of chemicals and bacteria but will have a higher level of inorganic dissolved solids, which RO systems are great at treating Reverse osmosis systems are also very efficient at removing potentially harmful pathogens and chemicals from private well water sources, cementing RO system’s effectiveness as a kitchen water filter solution or whole house well water filter.

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.

TOP PICK

OptimH2O Reverse Osmosis Claryum Under-Counter Water Filtration System with Chrome Finish Faucet

Aquasana OptimH2O

  • Harmful contaminant reduction: Y

  • Taste and odor reduction: Y

  • NSF certifications: 42, 53, 58, 401, P473

Runner up (reverse osmosis)

APEC RO-PH90

APEC RO-PH90

  • Harmful contaminant reduction: Y

  • Taste and odor reduction: N/A

  • NSF certifications: 58

Best flow rate and fluoride reduction

GE RO (GXRM10RBL)

GE RO (GXRM10RBL)

  • Harmful contaminant reduction: Y

  • Taste and odor reduction: N/A

  • NSF certifications: 58

Best value

Whirlpool RO System

Whirlpool RO System

  • Harmful contaminant reduction: Y

  • Taste and odor reduction: Y

  • NSF certifications: 42, 58

Best design

Brondell Circle RC100

  • Harmful contaminant reduction: Y

  • Taste and odor reduction: Y

  • NSF certifications: 42, 53, 58

What to look for in a Reverse Osmosis Water Filter

Contaminants removed

ContaminantsCertification to removeProducts
Harmful contaminants: Lead, Asbestos, Arsenic, Mercury, Cysts, VOCs etc.*NSF 53, 58Aquasana OptimH2O, APEC RO-PH90, GE RO System, Whirlpool RO System, Brondell Circle RC100
Chlorine and Chloramines/aesthetics issuesNSF 42Aquasana OptimH2O, Whirlpool RO System, Brondell Circle RC100
PFAsP473Aquasana OptimH2O
Emerging contaminantsNSF 401Aquasana OptimH2O

*Check with product performance data sheets if you are concerned about a particular contaminant.

The top factor in choosing a RO water filtration system is the number of contaminants removed, or how much of a specific contaminant a filter can remove.

If you are worried about the quality of your water and are unsure of what is in it, then you should aim for the best product available that eliminates the most contaminants possible.

If you know exactly what contaminants are in your local water source, you can be more precise in your purchase. For example, if your local water source has trace amounts of lead in it, then you will want a water filter that can filter over 99% of lead, and other contaminants may not be as much of a worry for you.

RO water filters commonly remove the following contaminants: chlorine, iron, lead, asbestos, TDS (total dissolved solids), bacteria, cysts, and fluoride along with many others.

We recommend finding out what contaminants are in your water source by checking your local Consumer Confidence Reports (CCR), or getting your private well water tested. This is because different systems remove different contaminants so choosing your product should be based on your specific needs.

Here are our main contaminants of concern and reasons why:

Lead:

There are 10.5 million lead services lines in the US feeding water into people’s homes and data is showing that nearly 30 million people drank from municipal water systems between 2015 and 2018 that violated the Environmental Protection Agency’s (EPA) Lead and Copper Rule. Contaminants such as lead can have dire health consequences and no level of lead is safe according to the World Health Organization (WHO). Additionally, in 2017 more than 500,000 children in the US have an elevated level of lead in their blood.

Chlorine:

Over 98 percent of the U.S. water supplies use chlorine to treat the water. That means roughly 98% of Americans drink tap water containing chlorine. Chlorine gives water a distinct and unpleasant taste as well as smell. A recent study in the International Journal of Cancer Management found that disinfection byproducts like chlorine can result in cancer development, especially in the liver and kidneys.

PFAS:

Are man made substances that repel water and oil, and are “forever chemicals” that don’t readily breakdown. They are used in a variety of commercial products and have begun to enter public water systems, and wells, as a result of improper disposal of products made using PFAS. It is believed that up to 110 million American’s could have PFAS contaminated drinking water, which can cause reproductive, developmental issues.

Arsenic:

It is estimated that 2.1 million people in the U.S. may be drinking well water that is high in arsenic as a result of industrial and agricultural pollution. This could be higher as 13 million households in the US use private wells as their water source. Arsenic can give rise to a plethora of health issues including cancer, heart disease, nerve issues, and more.

There are also many other contaminants (too many to list), but if you get an RO water filter you can do your best to protect yourself and your loved ones from any adverse health effects. 

Because of the potential for lead to get into your water through leaching from old pipes after it leaves the water treatment facility, we do not recommend any RO products that have not been certified or tested to reduce lead.

Certifications

Aquasana OptimH2O

OptimH2O Reverse Osmosis Claryum Under-Counter Water Filtration System with Chrome Finish Faucet

Main Contaminants reduced
Lead, Chlorine, PFAS, Arsenic, Asbestos, Cysts

NSF
42, 53, 58, 401, P473

Annual filter Cost
$155

Ease of use* (/10)
8/10

Number of contaminants
Min. 88

See on Amazon

APEC RO-PH90

APEC RO-PH90

Main Contaminants reduced
Lead, Chlorine, Arsenic, Fluoride, TDS, Barium, Copper

NSF
58

Annual filter Cost
$100

Ease of use* (/10)
7/10

Number of contaminants
Min. 11

See on Amazon

GE RO System

GE RO (GXRM10RBL)

Main Contaminants reduced
Arsenic, Lead, Copper, Cysts, Fluoride, Turbidity, Chromium

NSF
58

Annual filter Cost
$85

Ease of use* (/10)
7/10

Number of contaminants
Min. 14

See on Amazon

Whirlpool RO System

Main Contaminants reduced
Lead, Chlorine, Arsenic, Fluoride, Chromium, TDS, Turbidity, Cysts, Copper

NSF
42, 58

Annual filter Cost
$95

Ease of use* (/10)
8/10

Number of contaminants
Min. 26

See on Amazon

Brondell Circle RC100

Main Contaminants reduced
Lead, Arsenic Chromium, Chlorine, VOCs, Cysts, TDS, Fluoride, Slenium

NSF
42, 53, 58

Annual filter Cost
$180

Ease of use* (/10)
9/10

Number of contaminants
Min. 14

See on Amazon

To be sure filter systems are filtering out what they claim to, look for products that have NSF (National Sanitation Foundation) or WQA (Water Quality Association) certifications that are the gold standards in the USA for water filtration systems. NSF and WQA marks are meant to provide proof that a product was “impartially reviewed to established standards or guidelines,” states the NSF.org website.

NSF and WQA marks also confirm that product labels and their claims have been objectively verified by a trusted third party and demonstrate a company (or organization’s) commitment to quality, compliance, and safety. The mark, which is recognized in more than 180 countries around the world, has varying associated numbers that range from the automotive industry, retail products, lab equipment, nutritional products, sustainability, and of course, water, wastewater, and food safety. 

For Reverse Osmosis filters, look for the following certifications:

  • NSF 42: Is certification to reduce mainly aesthetic or non-health related issues. These include chlorine, taste and odor, iron, manganese, and zinc.

  • NSF 53 and/or NSF 58 – Are certifications to reduce or eliminate contaminants that have known negative health effects. NSF 53 products have a carbon filter and can reduce contaminants to various degrees depending on the quality of the filter. 

    These contaminants include heavy metals (e.g., lead), Cryptosporidium, Giardia, pesticides, herbicides, benzene, MTBE, radon, trihalomethane, and PCBs. NSF 58 refers to reverse osmosis (RO) membrane filters, which can remove perchlorate, fluoride, nitrate, nitrite, radium, bacteria, cysts, and heavy metals. It is important to note that carbon filters and RO systems have many crossovers, but they do not filter out all of the same contaminants, as such they can be used in conjunction with one another in the same system.

  • NSF 401 – This certification is for new and emerging compounds, mainly as a result of pharmaceuticals, herbicides, pesticides, chemicals, flame retardants, and detergents being found in tap water that were previously not present.

  • NSF P473 – Certification to reduce PFAS, including PFOS (perfluorooctane sulfonate) and PFOA (perfluorooctanoate). To make this claim the product must be below to EPA healthy advisory limit of 70 parts per trillion.

Look for multiple certifications when searching for a water filter, and make sure they line up with the contaminants you either know or suspect are in your water source.

Best overall

Aquasana OptimH2O Reverse Osmosis Under Sink Water Filter System

NSF: 42, 53, 58, 401, P473
Price: $208.99

After getting through our top factors in choosing a reverse osmosis system, which are contaminant removal and certifications to prove it removes contaminants we wanted to introduce you to our top-rated product. It ticks a lot of our boxes, and to be our top choice it had to.

OptimH2O Reverse Osmosis Claryum Under-Counter Water Filtration System with Chrome Finish Faucet

Pros:

  • Removes 99% of harmful contaminants including arsenic, lead, PFAS, and bacteria

  • Certified to NSF 42, 53, 58, 401 + P473

  • Compatible with well water systems

  • Large filtering capacity

  • RO + Carbon + Claryum + Remineralization

  • Value

  • 2 year warranty

Cons:

  • Slower flow rate than some RO models

The Aquasana OptimoH2O has impeccable filtering, here are some of the main contaminants it can reduce or remove:

  • Lead: 96.6%
  • Chlorine: 97.66%
  • Arsenic: 97.6%
  • Cysts: >99.99%
  • Emerging compounds: >94.2%
  • PFAS: 96%
  • Asbestos: 99%

Performance data sheet

Being tested and certified by the NSF to NSF/ANSI standards 42, 53, 58, 401 + P473, it is one of the most comprehensively certified RO systems available. 

The Aquasana OptimoH20 utilizes a reverse osmosis membrane to reduce 14 impurities, and a patented Claryum filtration method to reduce 60 other contaminants. The filtering process is finished by remineralizing the filtered water with healthy amounts of calcium, magnesium, and potassium, which provides alkaline, pH balanced water. Here is a breakdown of the 3 stages + remineralization:

  1. Carbon filtration: Reduces organic chemicals, VOCs and MTBE
  2. RO membrane filtration: Filters out dissolved solids smaller than 1 micron including heavy metals.
  3. Claryum filtration: Targets chlorine and chloramine (aesthetic issues)
  4. Remineralization: Healthy amounts of minerals are absorbed back into the purified water to raise the pH level to a balanced level.

The Aquasana OptimoH20 is also our best RO system water filter for well water. With over 13 million American households relying on well water for drinking, it’s important to keep the water you drink from your well clean. Well water can have microorganisms such as bacteria, viruses and parasites in it, as well as nitrates, heavy metals, organic chemicals, radionuclides, and fluoride. 

Essentially anything that can contaminate water can be in a well water source depending on where you live. The Aquasana filters 99% of bacteria, putting it in the top 1% of RO systems we assessed.

The filter life for the Aquasana Optimo is solid with the Carbon and Clayrum filters needing to be replaced every 6 months or 365 gallons, which will cost you ~$65. The RO membrane needs to be changed every 1-2 years according to Aquasana and will cost ~$60, and the remineralizer costs ~$30 and needs changing once a year. If you use less water in your home than you’ll only need to replace the RO membrane once every 2-3 years.

The total system and running cost (filter replacements) for 5 years will cost approximately ~$815, which is an amazing deal considering you are getting the best RO water filter on the market.

The system can give you up to 32 gallons per day, men require about a gallon of water a day, and women require just under 3/4 of a gallon a day according to the Mayo Clinic. So if you take this into account, it can provide enough drinking water for a large family.

Reverse osmosis systems require adequate water pressure to be able to function effectively. Before purchasing, you’re going to want to make sure you have at least 40 psi in your home.

If your home’s water pressure is below 40 psi, you’ll want to look for a RO model that has a booster pump. If your home uses well water, you’ll need to make sure the well pressure of the tank is set high enough to let the RO system work best.

Filter capacity depends on how much water you and yours are going to be using. Are you using it for drinking, washing, ice trays, or a combination of all three? Different systems filter different amounts so you’ll need to adapt accordingly. 

If you are just looking for an RO system to fulfill your drinking water needs, then get a system that gives at least 9 gpd. 

If you want to soak some dishes as well, then systems over 10 gpd will be better. And if you are a large family that will be using an abundance of filtered water, then a system that can filter over 30 gpd may be best. 

Some models promote being able to filter 400 gpd, but this is unnecessary, no one will use that much water in a day, and if you do, you’re likely being very environmentally irresponsible.

An unfortunate downside to RO systems is that they can create a lot of wastewater. 

Ideally you’ll want to look for systems with 1:1 to 3:1 ratios if wastewater is something you’re concerned with. Consumers can also find systems designed to reduce waste by repurposing it towards other hydro uses like gardening or dishwashing. 

Systems with 1:1 ratios that are certified are difficult to find, and often they do not make their performance data readily available. 

With reverse osmosis systems, the drain ratio average is 3:1. High ratios hover around 5:1, but to reduce many contaminants these systems usually need excess water to drain out contaminants.

We suggest you look for a model around the average 3:1 ratio, but don’t rule out higher ratio models, especially if you can repurpose excess water. We suggest using it for watering gardens.

Most RO systems require installation meaning a dedicated faucet and drain connection. If you’re a renter and can’t install a faucet or alter the already built-in plumbing, you’ll want to consider a countertop model, pitcher, or other filtration method. 

If you’re a homeowner and you’re willing to do minor alterations, the RO system will be a great and long-lasting filtration option. 

People with a ‘can do’ attitude and minor DIY skills will be adept at installing RO systems in a matter of minutes by following easy-to-follow instructions that come with every product. Some of which even offer instructional videos.

RO systems are designed to strip the water of not only its harmful contaminants, but also valuable minerals. The process makes the water slightly acidic, to restore pH levels some models offer remineralization. 

The remineralization feature inserts healthy and valuable minerals back into the water at the end of the filtration process. If you’re looking for healthy minerals in your water, consider models that offer remineralization.

RO systems have a wide-range of pricing with low-end products at $100 and “premium models”at $1,000. Marketing teams will try and lead you to believe that more expensive units offer more filtration stages that can filter more water at a time. This is however not always correct. 

We’ve found the best products or usually in that mid-range price category. Mid-range products will get the job done, and you won’t be spending needless $.  We recommend spending around $200-300 for the purchase of a reverse osmosis system. 

In addition, you’ll also want to take into consideration the annual cost of having a filter system, like individual filter replacements. You’ll likely save money on all the bottled water you won’t be buying anymore.

RO systems usually have multiple filters with different lifespans so it might be beneficial to protect your investment with a warranty. 

Some products offer multiple-year warranties and we’d recommend buying products with at least a one-year warranty. 

So, with all that said, here are some more of our best reverse osmosis systems to consider going forward. We tried to give you a range of specifics to help cover as much ground as possible.  

What makes under sink water filters different?

Truly on-demand

Thanks to the way they combine with your sink, these filters are sleek and highly versatile. A dedicated filter faucet makes it easy to fill glasses or pots for cooking with one hand.

Unlike pitcher filters, most models don’t use a reservoir—meaning there’s no annoying wait for water to feed through the system, RO systems can be an exception, but their holding tanks should be large enough that you never have to wait for water.

A step up in filtering power

Some under sink filters at lower price points use the same filtering mechanism as other kitchen designs. But the majority employ larger, more powerful filtration methods, harnessing mains pressure to push tap water through dense carbon blocks or reverse osmosis membranes (see below).

This leaves tap water purer, better tasting, and potentially safer than when using a pitcher or faucet-mounted solution.

Style considerations

Most under-sink models either send water directly through your pre-existing faucet or through a secondary tap, mounted around your sink. Here, many under-sink filters are supplied with their own water dispensers—but you don’t necessarily need to use the dispenser that comes out of the box. Sourcing your own faucet for an under-sink filter can add to the look of your kitchen, making the filter seem more integrated with your other appliances.

Runner up (reverse osmosis)

APEC RO-PH90

The APEC RO-PH90 performance data sheet is not readily available, however, we got in contact with APEC and they provided it upon request.

APEC RO-PH90

Pros:

  • Filtering capability

  • WQA Gold Seal certified to NSF/ANSI 58

  • Super capacity filters (long life)

  • Affordable filter replacements

  • Suitable for most houses

  • 90 GPD capacity

  • Remineralization

  • Large holding tank

Cons:

  • Only certified to one NSF/ANSI standard

Here are the contaminants it reduces:

  • Lead: 96.8%
  • Fluoride: 93.8%
  • Arsenic: 99%
  • Chromium: 99%
  • Copper: 98.4%
  • Turbidity: 98.7%
  • Barium: 98.8%
  • Cadmium: 98.3%
  • Radium: 98.8%
  • Selenium: 97.8%

The WQA has certified this product to NSF/ANSI standard of 58 so you know you are getting a quality under sink water filter that has been through rigorous independent testing. 

This is a 6-stage filtration system, meaning it has 6 different filters. Each stage has its own unique filtering capability: 

  1. Sediment filter: removes dust, particles, and rust.
  2. Carbon block filter: removes chlorine and chloramine and any associated odor and taste
  3. Carbon filter: removes VOCs and other common chemicals
  4. Reverse osmosis membrane: filters harmful contaminants including arsenic, lead, fluoride, chromium, radium and more.
  5. Coconut shell refining carbon: removes any residual taste from RO tank
  6. Calcium carbonate remineralization: increase pH level by adding calcium carbonate mineral back into the water.

That’s a lot of filters! Fortunately these filters can be purchased as a complete set. However, like most RO systems the filters need to be changed at different times, as some filters have shorter lifespans. The shortest is 1 year, and the longest is the RO membrane which lasts 3 to 5 years (depending on use). So you won’t be changing filters often. 

The price for 6 filter replacements is around $150, so it’s a great bang for your buck. The majority of under sink filters/reverse osmosis need filter changes at least once every 6 months, so this system is a step above. 

This system is suitable for houses with water pressure between 40-85 psi. This will cover the vast majority of homes water pressures, the average psi of homes is 50 and the maximum is 80. 

This model has a 4 Gal. storage tank, so when that is full the dedicated faucet flows freely. And the storage tank begins to refill as water is used.  The system can filter 90 GPD. For reference, it is recommended to drink ½ to 1 gallon of water a day per person, so if you have a large family it has you covered (and more). 

For the price of just under $350 this comprehensive system has all your drinking needs covered. The 5 year cost for this system including purchase is approximately ~$900.

Its ongoing costs (filter replacements) are low, so this system will be cheaper than most other under sink/reverse osmosis systems long term. 

The APEC comes with a 1-year warranty and lifetime technical support for peace of mind.

Best flow rate and fluoride reduction

GE RO System

The nice thing about the GE RO is that it has a high flow rate for a reverse osmosis system. Water flows freely out of its dedicated faucet at 1 gpm. You won’t be waiting around to fill up glasses of water, or any bottles. The typical water bottle is 16.9 oz. so if you had to fill one up it would take about 7.5 seconds to fill up, and you could fill up 8 bottles in a minute. Now you have bottles of water you can put in your fridge to last you a few days! All for less than a couple minutes of your time. If you’re filling up a glass of water it will take just a few seconds.

GE RO (GXRM10RBL)

Pros:

Cons:

  • Only certified to one NSF/ANSI standard

  • Lower daily production rate

Not only will you have water on demand, you’ll have quality filtered water. Being certified to NSF 58 to reduce the following contaminants:

  • Lead: 98.6%
  • Copper: 98.3%
  • Turbidity: 99.1%
  • Fluoride: 94%
  • Radium: 95.1%
  • Selenium: 97%
  • TDS: 94.7%
  • Cysts: 99.99%

Performance data sheet

Not only is this a quality system in terms of filtering, but it comes at an affordable price just under $150. Annual filter replacements will cost about $85, which is the lowest on our list. So for long term value this is a great reverse osmosis system. 

A slight downside to this system is that it provides less gallons per day than other systems on the list. But if you only plan on using this system for drinking and light washing then it will have you covered. Many systems provide a greater daily capacity than you could ever really use.

Best value

Whirlpool RO System

Our best value reverse osmosis system is Whirpool’s RO System. It’s approximate 5 year cost is $560, making it the lowest cost for 5 years on our list.

Whirlpool RO System

Pros:

  • Reduces harmful contaminants

  • Reduces odor and taste issues

  • WQA Gold Seal certified to NSF/ANSI 42, 58

  • Best value system

Cons:

  • Not certified to reduce PFAS or emerging contaminants

Low costs, but big filtering! This system performs just as well as other RO systems. It is certified to NSF 58 for the reduction of the following contaminants:

  • Lead: 99.1%
  • Arsenic: 98.2%
  • Fluoride: 96.5%
  • Turbidity: 99%
  • TDS: 90.6%
  • Chlorine: 95.2%
  • Copper: 98.8%

Performance data sheet

Not only is this product affordable, has great filtering, but it comes with a solid 2 year warranty. 

It provides more than adequate filtering capacity being rated to filter 18.46 gallons per day. A downside is that it does not offer remineralization.

Best design

Brondell Circle Reverse Osmosis System

The Brondell has a very different look than the majority of other RO systems. The entire system is tucked into a sleek-looking box, reducing the number of exposed tubes, resulting in a tidy-looking set up.  Besides its elegant look, this four-stage filter is one of the smallest systems on the market and is ideal for small households looking to optimize space.

Pros:

  • Removes harmful contaminants

  • Removes chlorine

  • Certified to NSF 42, 53, 58, 372

  • Beautiful design

  • Compact size

  • Easy storage

  • Easy installation

Cons:

  • Slow flow rate

  • Expensive filters

The Brondell Circle brands itself as being ten times more efficient than a lot of other RO systems on the market and it’s simple to install in a complete all-in-one system.

Besides being NSF 42, 53, 58, 372, and WQA certified, this unit is attractive enough that it makes you think it was designed to be a countertop system. Here are some of the contaminants that the Brondell can reduce/remove:

  • Lead: 98.2%
  • Copper: 98.7%
  • Fluoride: 83.8%
  • Chlorine: 98.4%
  • VOCs: 99.8%
  • Cysts: 99.96%

The under-sink system has a daily filtering capacity of 56 gpd and works at a 2:1 waste water ratio. The product has a one year warranty and considering its design is so respected, its $279.99 price tag isn’t too shabby either. 

The four-stage filtration system includes a chrome tap and faucet and features a sleek LED light to indicate when its filters need to be changed. 

Speaking of, the system uses multiple filters which range from $69.99 to $79.99. But again, consumers are coming to the Brondell Circle because of its design and we’ve chosen it as our best designed RO system.

Additional Information

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.