Richard Arconti 
Bacteria are tiny, single-celled organisms that exist everywhere on Earth, from the deepest oceans to the highest mountains. They play a vital role in the environment and are essential for human health. But bacteria can also cause disease, making them something that most people want to avoid. In fact, one of the main reasons people install water filters in their homes is to remove bacteria from their drinking water.
Reverse Osmosis (RO) is one of the most popular home water treatment methods. As a result, many people ask does reverse osmosis remove bacteria? The answer is, yes! Reverse osmosis is able to remove up to 99.9% of microorganisms from your water.
Reverse osmosis is able to remove not just bacteria but also other contaminants like arsenic, lead, chlorine, and fluoride. Keep reading to learn how effective reverse osmosis is at removing bacteria, how UV lights play a role, and what alternatives there are to treat bacteria and viruses.
How Does Reverse Osmosis Remove Bacteria?
Reverse osmosis is a filtration process used to remove impurities from tap water by forcing it through a semi permeable membrane. By using pressure to force water molecules through a membrane with a tiny pore size of approximately .0001 micron, only the smallest H20 molecules make it through.
The reverse osmosis filtration process will treat most types of bacteria and viruses in water including[1]:
- Bacteria: E. coli, coliform, salmonella, and Campylobacter
- Viruses: Norovirus, Hepatitis A, and Enteric
- Protozoa: Giardia, Cryptosporidium, and Trichomonas
As mentioned above, reverse osmosis removes not just bacteria but also other contaminants like arsenic, lead, chlorine, and fluoride. What’s left behind in the RO process are all these harmful contaminates that are then rinsed away leaving only purified water. RO filters are able to remove up to 99% of all contaminants from water, making them one of the most effective in-home water filtration methods available.
While reverse osmosis is not 100% effective at removing all bacteria from water, it is still one of the most effective home water filtration methods available. If you are concerned about the levels of bacteria in your tap water, a quality reverse osmosis system is the most practical solution.
Related: Best RO Systems For Bacteria Removal
Do Reverse Osmosis With UV Light Sterilize Bacteria?
There are many ways to sterilize bacteria, but one of the most popular methods is reverse osmosis with UV light. This method works by using a traditional reverse osmosis filter system to remove water contamination and then exposing the water to ultraviolet light to kill any remaining bacteria for a 99.9% sterilization rate.
With this method, it is critical to make sure the UV light is powerful enough to kill all bacteria. This means a UV dose in excess of 40 mj/cm2. There are a handful of RO systems with UV purification integrated into the system to meet those requirements. However, if you need to purchase a separate UV purifier light, make sure to install it after the filtration process. The reason is that any sediment in the tap water can block the light from passing through the water to effectively kill bacteria.
While a RO filter system system is extremely effective on its own, supplementing it with a UV sterilizer can ensure any remaining microorganisms are stopped in their tracks.
Do All Reverse Osmosis Systems Remove Bacteria?
No, not all reverse osmosis systems remove bacteria. We know that most RO membranes have pores that are .0001 microns. The typical size of bacteria ranges from about 1 micron to 5 microns.[2] Therefore, most ROs will treat bacteria to varying degrees.
There are a few key considerations to finding an RO system designed to remove bacteria. Start by looking for an RO system certified by the National Sanitation Foundation (NSF) to standard 58. The NSF is a leading independent organization that tests and certifies products, including water filtration systems.
If you have well water where bacteria and iron bacteria are prevalent, you will need a RO system for well water. That’s because heavy iron and sediment can foul RO membranes prematurely. Specialized reverse osmosis systems will have KDF filters or other features to handle well water while effectively treating bacteria.
All RO filter systems are also not created equal. Look at the quality of the RO membrane and the pore size it has. If they are too large, more contaminants will be able to pass through. If water quality is top of mind, it is important to choose an RO system that is designed to treat bacteria.
How Much Bacteria Does RO Remove?
Generally, reverse osmosis membranes will remove up to 99.99% of bacteria and viruses from your water.
The amount of bacteria that an RO system removes depends on the quality of the water that you are starting with. If your tap water is already very clean, then the RO system will remove nearly all bacteria. However, if your water is heavily contaminated or your system is not well maintained, the RO membrane will be less effective.
Furthermore, the type of bacteria that is in your water will also affect how much the RO system removes. Some bacteria are more difficult to remove than others because they are much smaller or have thick cell walls that protect them from low powered UV lights. For example, Giardia or Cryptosporidium.
However, if your RO membrane is well maintained and has a poor size of .0001 micron, you will have very high effectiveness close to 100%.
What is Not Removed by Reverse Osmosis?
RO systems are effective at removing a variety of contaminants, including heavy metals, minerals, and VOC, and more. However, there are some contaminants that RO systems cannot remove. Here’s a look at the two main contaminant categories that are not removed by RO membrane filtration:
- Dissolved Gasses: Carbon dioxide, hydrogen sulfide, and ammonia
- Organic Compounds: Formaldehyde, acetonitrile, and methanol
Dissolved gases can permeate the RO membrane so that they are not removed. If you want to remove organic matter from your tap water, the RO system should include a high-quality carbon pre-filter. That is why RO systems are so practical because they are able to remove most contaminants and harmful chemicals. But keep reading to see the disadvantages of ROs when it comes to water quality.
Drawbacks of Using Reverse Osmosis Systems
As we’ve seen, one of the main benefits of using a RO water filter system is the effective treatment of bacteria. However, there are also some potential drawbacks to using this type of system:
- High Initial Cost: While the initial cost of installing an RO treatment system may be higher than other water purification methods, the long-term savings and health benefits make it worth the investment.
- Maintenance Requirements: Like any other type of water filtration system, RO systems require occasional maintenance and replacement of filters. However, the frequency of maintenance will depend on the specific water system you have and the quality of your water supply.
- Slow Water Flow: Because a tank based RO filter system relies on storing the purified water in its tank, you may find yourself waiting for it to regenerate if you use all the water. This is not typically a major problem, but it is something to keep in mind. Tankless ROs utilize electric water pumps to have on demand water flow, so this is not an issue with them.
- Waste Water: Another potential drawback of a RO treatment systems is that they produce wastewater. On average, for every gallon of purified water produced by the system, there will be approximately 4 gallons of wastewater. With more efficient tankless systems, you can get up to 3 gallons of purified water with only one gallon of waste water.
- Removes Healthy Minerals: RO water filter systems are so effective at removing common contaminants, that they even remove healthy minerals!
Other Water Filter Options For Removing Bacteria and Viruses
A RO water filter system is not the only type of water filter that can purify water with bacteria present. Here are some other options:
- Ultra-violet (UV) light: You can find UV water filters that use light to kill bacteria and viruses. According to the CDC, UV filters can be effective at removing Cryptosporidium, a type of bacteria that can cause diarrhea.
- Carbon Filters: These filters are effective at removing many different types of contaminants, including bacteria and viruses. It’s important to note that carbon filters need to be replaced frequently in order to remain effective.
- Distillation Systems: This treatment process involves boiling water and then collecting the steam, which leaves behind bacteria and viruses. Distillation is an effective way to remove many different types of contaminants, including heavy metals.
- Ion Exchange: This type of water filter uses charged beads to remove contaminants, including bacteria and viruses. Ion exchange is often used in commercial settings, such as water treatment plants.
FAQs For Reverse Osmosis Bacteria Removal
Are reverse osmosis that remove bacteria expensive?
No, not at all. In fact, many home RO water filter systems are very affordable. As with any technology, there are always going to be higher-end models that cost more, but RO is not an unrealistic expense by any means. The exception to this rule would be if you go with a whole house reverse osmosis system, which are relatively more expensive.
Does reverse osmosis remove coliform bacteria?
Yes, RO filter systems are very effective at removing coliform bacteria from water. This is one of the main benefits of using RO to purify tap water, as coliform bacteria can cause serious health problems if ingested.
Does RO remove bacteria from drinking water?
Just about all RO systems are designed to treat bacteria in tap water. This means that you can have peace of mind knowing that your pure water is free of harmful bacteria when you use an RO system.
Is there a way to remove bacteria in tap water without RO?
There are a few different methods that can be used to treat bacteria in drinking water, but RO is generally considered to be the most effective. This is because RO filter systems are designed to remove all types of impurities from tap water, including bacteria. If you are looking for a way to get pure water without using RO, you may want to consider using a UV filter, which has a very high effectiveness at removing bacteria.
Do tankless ROs have less bacteria than tank based ROs?
The filtration process of removing bacteria is the same in both tankless and tank ROs. The difference is that tank based systems can lead to bacteria growth in the tank itself. So as water passes through the tank, it may become compromised.
