Is UV Required With Reverse Osmosis (RO)?

Ultraviolet (UV) light presents a potent weapon against waterborne germs like viruses and bacteria. But the question arises: is it a necessary addition to a reverse osmosis (RO) system?

UV sterilization is required with a Reverse Osmosis system to kill bacteria, viruses, and algae from the water supply or from the RO holding tank. RO systems alone remove more than 90% of sediments, chemicals, and heavy metals but do not remove microbes.

In this article, we’ll delve into different types of UV light, UV sterilization, RO water purification, and why you might want both.

The Importance of UV with RO

To appreciate the need for UV sterilization alongside your RO system, it’s crucial to evaluate your water supply’s quality. If your goal is to rid your water of soluble and insoluble contaminants, an RO purification system is your go-to choice. However, if you’re concerned about microorganisms, UV sterilization becomes a must.

Total Dissolved Solids (TDS)

TDS, which includes nitrates, calcium, sodium, potassium, chlorides, sulfates, and carbonates, measures the volume of dissolved contaminants in water. According to the World Health Organization, water with less than 300 mg/L of TDS is deemed excellent-tasting, while 500 parts per million is acceptable for drinking. An RO filter can effectively eliminate these contaminants, especially if your water source is hard and has a high TDS value.

Microorganisms: Bacteria, Viruses, and More

Water from sources like reservoirs, rivers, ponds, wells, or even tap water can carry a multitude of organic contaminants and microorganisms. To tackle this, you’ll need an additional UV filter after your RO purification or an RO system equipped with built-in UV technology. This extra step ensures your water is free from harmful bacteria, viruses, and other microorganisms.

Furthermore, if your RO holding tank isn’t properly maintained, it can become a breeding ground for bacterial and algal colonies. Running the water through a UV disinfection system can rectify this, making your water safe for consumption.

In summary, while an RO filtration system is excellent at removing many contaminants, only a UV filtration system or an RO system incorporating UV light can effectively exterminate bacteria, viruses, and algae in your water.

Understanding UV Light Types

Ultraviolet (UV) light encompasses non-ionizing radiation with wavelengths between 100 and 400 nm. While natural UV from the sun can have adverse effects on the skin (UVA and UVB), artificial UVC light is harnessed for water purification due to its potent germicidal properties. UVC light penetrates and attacks bacteria, viruses, yeast, spores, and even algae, making it a formidable tool for disinfection.

UV Sterilization Process

The UV purification process is straightforward—a UVC lamp with a wavelength between 240 and 280 nm comes into contact with water for 10-20 seconds, effectively killing most microbes. This method doesn’t require the addition of chemicals or disinfectants, preserving the water’s taste and smell. UV purification is also faster and more cost-effective to maintain than RO filtration.

However, it’s important to note that UV alone doesn’t remove dissolved or suspended salts, making it less suitable for addressing issues like turbidity (cloudiness) in water.

RO Filtration Process

Reverse Osmosis (RO) filtration employs a semi-permeable membrane to filter out suspended solids and dissolved contaminants. This process, which requires electricity and periodic filter replacements, removes minerals from hard water and various impurities, making it suitable for improving taste and clarity.

However, RO filtration cannot eliminate bacteria and viruses due to their small size, and it generates water wastage during the flushing of contaminants.

RO UV: The Best of Both Worlds

The RO UV filtration mechanism combines the strengths of both RO and UV. It removes dissolved minerals, suspended particles, bacteria, viruses, and other contaminants, resulting in disinfected water with reduced Total Dissolved Solids (TDS).


RO UF (reverse osmosis/ultrafiltration) systems incorporate ultrafiltration to remove suspended solid particulate matter, making water clearer. While UF is faster and generates no water waste, it can’t tackle bacteria and viruses or dissolve impurities. In contrast, RO UV systems effectively address a wider range of contaminants, making them the superior choice for comprehensive water purification.

In Conclusion

Pairing UV purification with RO filtration ensures the removal of a broad spectrum of contaminants, making your water safe for consumption. This two-pronged approach effectively eliminates microbes, dissolved contaminants, and suspended solids, leaving you with clean and healthy water.

Theresa Orr

Theresa Orr is an Earth Scientist who specializes in determining past climates from rocks using geochemistry. Her passion for clean water drives her to breakdown the science to provide easy to understand information that everyone can read.

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