EDUCATION | COASTAL WATER

Reverse Osmosis System and LED UV Light

Do you need UV with a Reverse Osmosis System?

It depends on your water.

Reverse Osmosis (RO) removes dissolved contaminants, but it does not disinfect microorganisms. UV systems neutralize bacteria, viruses, and other microbes, which is why many commercial water systems combine both technologies.

Whether you need UV alongside RO depends on your water source, system design, and biological risks present in your supply.

In this article, you’ll learn when UV is necessary with an RO system-and when RO along may be sufficient.

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Do you Need UV With Reverse Osmosis?

Sometimes- but not always.

You may need UV with a reverse osmosis system if:

• Your system uses a storage tank

• You water source is well water

• You want protection against bacteria and viruses

• Your RO system removes chlorine but does not disinfect water
  

You may not need UV if:

• You water supple is consistently treated municipal water

• You system is tankless

• Biological contamination risk is low

Because they solved different problems, many commercial systems combine RO filtration with UV disinfection.

How Reverse Osmosis Removes Chemical Contaminants

RO forces water through a semi-permeable membrane — a physical barrier with pores small enough to block most dissolved solids.

A properly functioning RO system can remove up to 99% of many dissolved contaminants, including:

• Heavy Metals such as lead, arsenic, and mercury

• Chlorine and disinfection by products

• Nitrates from agricultural run off

• Fluoride

• Pesticides and industrial chemicals

• Dissolved Solids that affect taste and color

Because of this capability, RO is widely considered one of the most effective technologies for removing chemical contamination from drinking water.

But there is one gap many RO systems do not fully address.

The Biological Gap RO Doesn't Fill

Microorganisms behave differently than dissolved chemicals.

Many bacteria are large enough to be physically blocked by an RO membrane. Viruses, however, are much smaller.

Many viral particles (0.02–0.3 microns) can potentially pass through membranes, particularly as membranes age or develop microscopic defects.

There's a second, less obvious issue.

RO removes the residual chlorine that municipal water uses to suppress bacterial growth in distribution lines. Once that chlorine is removed, the filtered water no longer has that biological protection

An RO storage tank is typically:

• Dark

• Wet

• Chlorine Free

Those conditions can create a favorable environment for bacterial growth if the system is not regularly sanitized.

Can Viruses Pass Through Reverse Osmosis Membranes?

Sometimes.

Reverse osmosis membranes can block many microorganisms, but they are not designed to disinfect water.

Viruses are extremely small—often 10–100 times smaller than bacteria—and can potentially pass through membranes or enter water through small system defects or storage tank contamination.

For this reason, systems that require protection against biological contamination often include a UV disinfection stage after RO filtration.

How RO and UV work Together

RO handles chemical contaminants. UV handles biological risks.

Used together, they provide broader protection than either technology alone.

How UV Closes the Gap

UV purification works differently from filtration.

Instead of physically removing contaminants, UV-C light (254 nm) disrupts the DNA and RNA of microorganisms, preventing them from reproducing or causing infection.

UV systems are effective against:

• Bacteria

• Viruses

• Protozoa

They also have several advantages:

• No chemicals added to the water

• No effect on taste or odor

• No disinfection byproducts

• Minimal maintenance (typically annual lamp replacement)

Because UV systems operate at the point of use, water that has been sitting in a storage tank is disinfected again just before it reaches the tap.

It's important to understand that UV does not remove microorganisms—it permanently disables them.

Does Your Business Actually Need UV?

You are more likely to need UV if:

• Your RO system uses a storage tank (most do)

• Your building uses well water

• Your business serves water directly to customers or employees

• Your system is older and hasn't been sanitized regularly
  
  

RO alone may be sufficient if:

• Your water source is consistently treated municipal water

• Your system is tankless

• Filters and membranes are replaced on schedule

• There is no elevated biological contamination risk
  
  

If you're uncertain, combining RO and UV is often the safest approach.

The cost of having UV when you don't strictly need it is small. The cost of needing it and not having it can be significant.

The Bottom Line

Reverse osmosis is extremely effective at removing chemical contaminants from water. However, it does not fully address biological risks such as bacteria and viruses—especially in systems that use storage tanks.

UV disinfection fills that gap by neutralizing microorganisms before water reaches the tap.

For many commercial systems, combining RO filtration with UV disinfection provides the most complete protection.

Before You Talk to Any Water Filtration Company (Including Us)

Shopping for drinking water in your office? Start with the right questions.

Download our Drinking Water in the Workplace Checklist. It will help you:

• Understand the basics of where your water is coming from

• Define the details of your current water dispenser

• Evaluate the relationship between your current vendor
  
  

This will help you take a deeper dive into optimizing and elevating your current water systems in the workplace

→ Download the Free Checklist

Related: Understanding Water System Pricing- learn about the systems you’re investing in here