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Reverse osmosis and UV filtration are among the most effective water purification methods available. So, it’s no surprise you’ll find these purifiers installed in homes, restaurants, and commercial applications worldwide.
Unfortunately, due to a lack of awareness about how the two types of water systems work, UV filters are sometimes installed in applications better suited to RO filters and vice versa. Exaggerated claims made by some product manufacturers don’t help the situation either!
Luckily, a little basic knowledge about reverse osmosis and UV water disinfection should help you pick the right one.
So, reverse osmosis vs UV filtration – what are the differences, and which is best for your needs?
UV and RO are both best-in-class water filtration systems, but they are used to accomplish different results. UV filters are built for eradicating waterborne pathogens, while RO systems eliminate a wide array of overall contaminants.
While RO systems are somewhat effective against microbial contamination, they are nowhere near as effective as UV filters – which can eliminate over 99.9% of harmful microorganisms.
A reverse osmosis system exceeds at removing heavy metals, salts, pesticides, water disinfectants, disinfection byproducts, PFAS, and most other water pollutants.
Both filter systems are low maintenance and relatively inexpensive, but UV filters are even cheaper and easier to maintain.
UV and RO systems can also be used in conjunction to achieve a greater water purification level than when used alone.
What Is Reverse Osmosis Water Purification and How Does It Work?
Stated simply, reverse osmosis purification is a method of filtering water by forcing it through a semipermeable membrane to capture even the tiniest of contaminants.
RO systems are unparalleled at capturing these fine particles. In fact, they can trap contaminants down to just .0001 microns, which is finer than what any other water filter can achieve.
In addition to the semipermeable membrane – which is the primary filtration stage – RO systems feature several pre and post-filters. The two most common are a sediment filter to remove larger particles before they can reach the membrane and a carbon filter to remove chlorine/chloramine/chemicals and improve the water’s taste.
Benefits & Drawbacks
The biggest benefit to a reverse osmosis system is the superior level of filtration you’ll achieve. They remove up to 99.9% of lead, nitrites, arsenic, fluoride, chlorine, chloramine, disinfection byproducts, PFAS, chromium 6, VOCs, and so much more.
While they aren’t the absolute safest solution for removing biological contaminants like bacteria and viruses, many will do a solid job at these as well.
Most RO systems are surprisingly easy to maintain too, only requiring filter changes every 6 months or so and membrane replacement every 2 to 5 years. Under sink units are also fairly easy to install yourself as long as you’re comfortable with a little basic DIY.
As far as drawbacks, standard RO systems do produce so-called “wastewater” at a ratio of about 4 parts waste to 1 part filtered drinking water. This waste is a byproduct of the filtration process – which separates the water into a clean drinking stream and a contaminant-filled stream while it passes through the reverse osmosis membrane.
Besides, RO water loses somewhere between 85% and 98% of its mineral content, depending on the specific mineral. This is simply an unavoidable part of the RO process, so your filtered water will have less minerals than before filtration. An easy fix to this is adding a remineralization filter to your RO system which adds back healthy minerals like calcium, potassium, and magnesium.
What’s a UV Water Filter and How Does It Work?
A UV water filter uses UV light exposure to rapidly eradicate harmful microorganisms inside your water supply. UV-C light is extraordinarily effective at wiping out any microbes – as it effectively scrambles their DNA which kills them off with up to 99.9999% effectiveness.
The UV filter unit is typically a simple tube attached to a home’s water supply with a long UV bulb inside of it. As water flows through the tube it’s exposed to UV light, which renders any harmful microorganisms in the water harmless.
Most residential UV water filters are installed at the water supply to the entire home making them whole house systems, although point-of-use units installed at the kitchen sink are also popular.
Benefits & Drawbacks
The biggest benefit of a UV water filter is its tremendous effectiveness in eliminating organic contaminants including bacteria, viruses, and cysts. Other water purification methods can’t compete here, so UV systems are preferred when there is any possibility of biological contamination.
Additionally, because UV filters use an incredibly simple design, they are very low maintenance. The only required maintenance tasks are changing the UV light bulb every 12 months, occasional cleaning of the quartz glass sleeve that encases the bulb, and replacement of said sleeve every 2 years.
While UV systems are unmatched when it comes to killing germs in water, they are not effective at removing anything at all. This means they cannot actually filter contaminants out of the water.
The presence of solid bits and pieces floating in the water will render UV disinfection less effective – as microorganisms will survive if they’re shielded by nearby particles. This is why water should typically be filtered before it gets to the UV filter. The same issue applies with high water hardness levels.
Lastly, a UV filter will not work without power. This won’t be a major drawback for most people, but something to be aware of should your power go out unexpectedly.
Differences Between UV and RO Water Purifiers
As you can probably guess by now, UV and RO water treatment serves different purposes, so the overlap between them is fairly small. However, deciding which one is right for you can be a tricky task in some cases.
Let’s take a look at the differences between UV and RO water purifiers.
Contaminant Reduction
Both UV and RO filters are incredibly effective at what they do, the only difference is the type of contaminants eliminated.
UV filters are only effective at eliminating organic contaminants – think bacteria, viruses, protozoa, and cysts (in some cases even fungi and algae). That said, they are incredibly effective at eliminating these – up to 99.9999% in ideal conditions.
As mentioned previously, they aren’t effective at eliminating any other contaminants, so any chemicals, heavy metals, VOCs – you name it – present in the water will remain after passing through the filter.
In contrast, RO systems are effective against a broad range of contaminants including metals, chlorine/chloramine, minerals and salts, pesticides, sediment, and nitrates/nitrites.
They are generally effective against microorganisms, but not to the degree that a UV is. Also, in rare cases, germs can grow and colonize an RO system’s filters or storage tank, which is one reason why they should be sanitized regularly.
Cost
A typical under sink reverse osmosis system will run you between $150 and $600. That said, price shouldn’t be the only consideration when shopping for a water filter, as many lower-priced units perform effectively.
Higher-end units will feature more sophisticated filtration, add-ons like remineralizers, pressure pumps to reduce wastewater, and NSF certifications.
As far as yearly maintenance costs are concerned, you’re looking at approximately $50 to $200. This will cover sediment and carbon filter replacements as well as membrane replacement.
A point-of-use UV system is significantly less expensive – running about $70 to $200. The main difference in price for these units will be the intensity of the UV bulb.
Yearly maintenance costs for a UV system typically run between $100 and $150. This includes the cost of yearly lamp replacement as well as quartz replacement every 2 years.
Maintenance
Reverse osmosis systems are fairly easy to maintain, but neglecting to perform scheduled maintenance can lead to the system running slowly or ineffectively.
The main tasks that need to be performed regularly are changing the pre and post-filters, replacing the membrane, and cleaning/sanitizing the storage tank.
Sediment and carbon filters should be changed every 6 to 12 months, depending on your model. The RO membrane lasts much longer and only needs replacement every few years.
The storage tank should be cleaned and sanitized once or twice a year, so doing this at the same time you replace the filters makes sense. Also, make sure that storage tank pressure is rightly calibrated.
Because of their simple design, UV filters require even less maintenance than RO systems. The main tasks to be performed are changing the UV light bulb, cleaning the quartz sleeve, and replacing the quartz sleeve when it becomes too foggy.
UV light bulbs lose effectiveness over time, and after 9,000 hours their effectiveness is down to about 60%. Yearly replacement will keep the system running optimally and prevent you from consuming contaminated water.
The quartz housing surrounding the bulb tends to fog up over time, so it should be cleaned every 12 months, more if you’re in a locale with hard water. But even if you are cleaning it regularly, the quartz will eventually fog up permanently and thus should be replaced when this occurs – about every two years.
Wastewater is a by-product of the RO filtration process, so reverse osmosis systems will consume significantly more water than UV water purifiers which waste no water at all.
While the typical wastewater to filtered water ratio with RO is 4:1, this can be reduced to 1:1 by using a permeate pump. Booster pumps can reduce the waste even further – to as little as 0.2:1.
All Differences at a Glance
Criteria
Reverse Osmosis Systems
UV Filters
Microbial Disinfection
Somewhat
Complete
Water Disinfectants + Byproducts
Yes
Usually No
VOC Removal
Yes
No
Pesticide Removal
Yes
No
Overall Chemicals
Yes
No
Mineral/Salt Removal
Yes
No
Metal Removal
Yes
No
Sediment Removal
Yes
No
Overall TDS Removal
Yes
No
Unit Cost
$150 – $600
$70 – $200
Annual Maintenance Cost
$50 – $200
$100 – $150
Maintenance Difficulty
Moderate
Easy
Wastewater
Yes
No
UV Filtration vs. Reverse Osmosis – Which Is Better for Your Filtration Needs?
Now that you have a solid understanding of how both of these filters work, choosing the right one for your needs should be a breeze!
When to Use UV? For Disinfection!
Put simply, if you’re looking to disinfect your water of any potential biological contamination – you can’t beat a UV filter.
UV filters are the cream of the crop for this type of application, with effectiveness at eliminating pathogens above 99.9%. They’re also very low maintenance and inexpensive – which doesn’t hurt their case.
When to Use RO? For Contaminant Removal!
If you’re more concerned about contaminant removal, then an RO system is the way to go. RO systems remove an extraordinarily wide range of pollutants, so if your primary concern is anything other than biological contamination, you’ll be safe with a good RO filter.
What If I Already Own a Reverse Osmosis System?
If you already have an RO system installed and are worried about microorganism contamination, one solution is adding a UV filter to your existing system.
Some RO system manufacturers sell optional UV filter upgrades that can be added to an existing system.
Alternatively, you can install UV as the final post-filter stage. The water flow is slow at this point of the RO system, so a simple 1-gallon per minute UV filter would be adequate.
If you have any questions about reverse osmosis vs UV filter systems please don’t hesitate to leave a comment below!
About the Author Gene Fitzgerald
Gene Fitzgerald is one of the founders of BOS and currently head of content creation. She has 8+ years of experience as a water treatment specialist under her belt making her our senior scientist. Outside of BOS, Gene loves reading books on philosophy & social issues, making music, and hiking.
Learn more about Gene and the rest of the BOS Team.
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Leave a Comment:
Steven Ringstad says
April 22, 2023
We have just installed a 135000lt water tank to connect to our house. We are looking to fit a hole of house filter system between the rain water tank and the inlet to the house, what is your preferred system.
