What Is an RO UV Water Purifier and How Does It Work?

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Reverse osmosis systems are widely considered one of the best when it comes to home water filtration due to their wide spectrum efficacy and modest price.

While these filters are effective against nearly all contaminant types, they aren’t ideal for eliminating microbial contamination in water. UV filters are the ideal choice in this situation – as they’re effective at eliminating over 99.9% of waterborne microorganisms.

Luckily, you aren’t limited to one filter or the other. Many high-end RO system manufacturers offer systems incorporating UV filtration as one of the treatment stages. This means you’ll get the best of both worlds – a complete RO system to eliminate contaminants like heavy metals and chemicals, plus a UV filter to kill any harmful microbes.

But how does that work exactly?

Key Takeaways

  • RO UV water purifiers combine the wide spectrum contaminant filtration of traditional reverse osmosis systems with the near-total microbial elimination of ultraviolet light water filters. This results in drinking water you can have 100% confidence in.
  • Most RO UV systems utilize a UV filter as one of the later filter stages –after the sediment and carbon pre-filters as well as the RO membrane.
  • UV water filter performance is negatively affected by the presence of floating particles in the water. RO UV filters eliminate any suspended particles in the pre-filter and membrane stages, which ensures the UV filter can work optimally.

What Is an RO UV Water Purifier?

So, what is an RO UV water purifier?

An RO UV water purifier is a complete reverse osmosis system which incorporates a UV light as one of the later filtration stages.

What RO Means

RO stands for reverse osmosis, which is the process of filtering feed water through a semipermeable membrane to reject contaminants. These membranes are ultrafine, so they can capture particles down to .0001 microns – which is far tinier than what other home water purification methods are capable of.

In addition to the semipermeable membrane, RO systems feature several other filtration stages to remove even more contaminants, especially those that could damage the membrane and affect water taste.

Most RO systems will feature both a sediment pre-filter to remove large particles as well as one or more carbon pre/post-filters to remove chlorine and chloramine and other chemicals, heavy metals, etc.

Different Water Filter Cartridges and Membranes

What UV Means

UV refers to ultraviolet light, which is the same electromagnetic radiation created by the sun.

In the context of water filtration, UV refers to filtering water past a UV light to eradicate any microorganisms inside it. UV light is incredibly deadly to organic contaminants like bacteria, viruses, protozoa, and cysts. It effectively scrambles their DNA – killing them instantly.

Keep in mind while UV will eradicate these microorganisms, it doesn’t remove them from the water. They will remain harmlessly suspended unless they’re removed using another filtration method.

Another thing to consider is that UV filtration effectiveness is lessened by the presence of suspended particles in the water. Microorganisms can survive passing through UV light if they’re shielded by these particles. This is why many standalone UV systems feature some type of sediment pre-filter – or an entire RO system!

How Does an RO UV Water Purifier Work?

An RO UV water purifier is essentially a normal RO system with a UV light filter added on.

The UV filter is typically added on after the water has passed through the various pre-filters and the reverse osmosis membrane. This ensures the water is particle-free so the UV filter can work effectively.

The Purification Process

RO systems use a number of filtration stages to achieve incredibly pure, clean tasting water. Let’s take a look at these stages in detail.


As mentioned previously, RO systems utilize multiple pre-filters to clean the feed water before it can reach the RO membrane. These filters remove large particles and chloramine/chlorine – both of which can damage the membrane – among other stuff.

Typically, the first pre-filter will be asediment filter. This filter will trap any large particles of sand, soil, rust, and other sediment suspended in the water.

The next pre-filter will be one or more carbon filters. Activated carbon has a large surface area which attracts contaminants like chlorine, pesticides, and VOCs. These filters also help enhance the taste of water, which is why a final carbon post-filter is often used to remove residual tastes.

Reverse Osmosis Membrane

After the pre-filtration stage(s) are complete, water flows through the reverse osmosis membrane. This stage is the heart of any RO system and removes any remaining contaminants like heavy metals, minerals and salts, pesticides, fluoride…

The reverse osmosis process works by utilizing hydraulic pressure (the water pressure in your feed water) to force the “dirty” water through the membrane. When it passes through the membrane, any contaminants are rejected at the entry side of the membrane, and low concentrate drinking water flows to the next stage.

Because the system relies so heavily on water pressure, you need at least 40 psi, and ideally 60 psi. If low water pressure is an issue, you can always install a pump to increase it.

UV Stage

After passing through the RO membrane, water flows to the UV filter stage.

UV filters use a simple but highly effective design. They’re tube-shaped units with a long UV bulb held inside a clear quartz housing.

As water flows through the tube it’s exposed to UV rays from the bulb – instantly killing any microorganisms contained within it.

UV Lamp

The UV lamp does the hard work in any UV filter. Most of these bulbs operate at 254 nanometers (nm), which is the ideal wavelength of UV-C light to fully eradicate microbial contaminants.

The bulb is mounted inside the middle of a stainless steel chamber and water flows around it. This ensures proper exposure to UV rays.

Quartz Glass Sleeve

The UV bulb is housed inside a clear quartz glass sleeve. Quartz is used instead of regular glass because it allows for a higher level of UV light transmission.

While quartz works well for UV light transmission, it does tend to fog up over time. Regular cleaning is necessary to keep the filter working effectively.

Reactor Chamber

The reactor chamber is the outer tube that houses both the quartz sleeve and the UV bulb. Water flows through the reactor chamber and around the bulb to disinfect it.

Activated Carbon Post-Filter

All RO systems I know feature a final carbon post-filter before the drinking water flows to the faucet. The purpose of this filter is to remove any remaining contaminants and ‘polish’ the water’s taste.

What Does RO + UV Water Purification Remove?

As mentioned before, a reverse osmosis system with a UV filter stage gives you the best of both worlds when it comes to water purification. Because RO filters and UV filters target different contaminant types, combining the two in a single system gives you the best filtration results possible.

The RO system will be effective against a broad contaminant range removing heavy metals, VOCs, pesticides/herbicides, minerals and salts, sediment, chlorine/chloramine, nitrates/nitrates, as well as many other organic and inorganic contaminants.

UV water filters target a much narrower range of contaminants, only being effective against microorganisms, mos importantly bacteria, viruses, and cysts. That said, they are unmatched at this task and can kill well over 99.9% of germs.

Keep in mind that UV filters use UV rays to disrupt the DNA of microbes – killing them and rendering them unable to reproduce. The dead microbes will remain in the water, but they are harmless at this point.

Under Sink Reverse Osmosis System

Benefits and Drawbacks of RO UV Water Purifiers

The primary benefit of an RO UV water purifier is the level of filtration you’ll get when combining these two outstanding filtration methods. RO systems are second to none when it comes to broad-based contaminant removal, while UV systems provide targeted elimination of microbial contamination.

Standalone RO systems aren’t ideal for microbial removal – and in some cases, bacteria can even colonize their storage tanks.

Both standalone RO and UV systems are fairly low maintenance, so combining the two means you’ll have a little more required maintenance than a standalone system but nothing too bad.

As far as drawbacks are concerned, RO systems as part of the filtration process produce wastewater. This is simply the contaminant-filled water that flows down your drain instead of passing through the RO membrane.

Typical RO systems produce about 4 parts wastewater to one part clean drinking water. This issue can be mitigated by installing a pump – which reduces this ratio to 1 part wastewater to one part drinking water or even less.

Lastly, RO water loses approximately 85% to 98% of its mineral content depending on the mineral in question. While this is less of an issue than some people make it out to be, you can always add a remineralization filter to your RO system to add back healthy minerals like magnesium, potassium, and calcium.


If you want your RO UV filter to continue working efficiently and effectively, then keeping up with scheduled maintenance is a must.

The main tasks that should be performed regularly are changing the pre and post-filters, replacing the membrane on schedule, cleaning/sanitizing the storage tank, regularly cleaning the quartz sleeve, replacing the UV bulb on schedule, and replacing the quartz sleeve when it becomes too foggy.

Sediment and carbon filters generally need to be changed every 6 to 12 months, but make sure to check your filter’s documentation to be sure. Most RO membranes have a lifetime of 2 to 5 years, after which they will need to be replaced.

The RO storage tank also needs regular cleaning and sanitizing to keep it sanitary and prevent any microbial accumulation. This should be done every 6 to 12 months.

As far as the UV filter stage is concerned, most bulbs lose their effectiveness after about a year, so they should be replaced annually to keep the system functioning optimally.

The quartz sleeve will also need regular cleaning to remove fogginess that builds up over time. This should be done once or twice a year.

Lastly, the quartz sleeve will need replacement every two years or so. Even if you clean it regularly, it will eventually fog up permanently.

When and Why to Use a Reverse Osmosis + UV Light System

While RO systems are highly effective at removing the vast majority of contaminants, one area they don’t excel at is removing microbial contamination. Conversely, UV filters excel at eliminating any microbial contamination.

If you’re in the US and have your water supplied by a municipal water company then the odds of microbial contamination are very low. However, if your water comes from a well, then the odds are significantly higher, and having a UV filter to eliminate potential microbes makes a lot of sense.

Giardia lamblia parasite

In either case, if you want to be 100% sure your water is completely clean and safe to drink, an RO UV system is the way to go.

If you have any questions about how an RO UV water purifier works 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.
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