Does UV Light Kill Bacteria in Water? (You Might be Surprised)

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Wondering whether UV light disinfection kills bacteria in water? We’ve shared everything you need to know in this guide.

🦠 Can UV Kill Bacteria?

So, does UV light kill bacteria? Technically, yes – as long as the UV light intensity is strong enough.

UV treatment doesn’t kill bacteria in the sense that you might imagine. There’s no zapping, laser-like behavior that fries the microorganism into nothingness. But the process is similar.

A UV disinfection system emits ultraviolet light. These UV-C rays penetrate the cell walls of pathogens like bacteria and scramble their DNA. This doesn’t technically “kill” the microorganisms. Instead, it prevents them from functioning and reproducing.

You can probably remember from your school days that bacteria need to reproduce to cause disease in the human body. So, if bacteria are unable to reproduce, they’re unable to cause any harm – and they’re effectively “killed”.

UV disrupts dna of microorganisms

🧫 How to Know if a UV System is Killing Bacteria

UV disinfection is an invisible process. Yes, the bulb emits a visible light, but there’s no way to tell by sight that the system is working (and you shouldn’t look directly at a UV-C bulb, either).

If you’re hesitant to trust that your UV water treatment unit is doing its job, you might be tempted to get your water tested before and after installing the unit at your plumbing system. However, because UV systems don’t physically remove bacteria when they disinfect water, a test may still detect bacteria after the water disinfection process – even if that bacteria is harmless.

water testing with tap score

So, how do you know if a UV system is killing bacteria in your water? There are two things you can do:

Check that the UV Light is Plugged In and Working

If your UV light is plugged in and switched on, then the system should be doing its job.

Over your years of owning a UV system, periodically check that the water treatment equipment is still in good order. Repair or replace damaged or worn parts as needed. If you’re doing all the right things to look after the system, you can feel reassured that it’s killing bacteria in your water.

Check that the UVC Light Doesn’t Need Replacing

Most UV-C products are powered by mercury. As a UV lamp reaches the end of its lifespan, its supply of mercury vapor will diminish. This will decrease the UV dose, and the UV system may be unable to effectively disinfect your water.

Make sure to replace the lamp whenever you’re due a lamp replacement. This is the best way to stay reassured that your UV-C system is killing bacteria in your water supply.

Installing uv-c lamp in uv water purification system

📋 Factors that Affect Whether UV Light can Kill Bacteria

Now we’ve established exactly how UV light can “kill” microbes like bacteria, let’s look at some of the factors that might hinder the ability of UV radiation to disinfect your water.

Contaminants Present in Water

The more contaminants your drinking water contains, the less effective the UV disinfection process.

This is due to something called “shadowing”. Sediment and heavy metals, which are much bigger than microorganisms, block the microorganisms from direct exposure to the UV rays. As a result, the UV radiation doesn’t fully disinfect the water.

Contaminants in your water, such as hardness minerals, can also build up on the glass sleeve that surrounds the UV light bulb. This means that the light can’t pass seamlessly through the glass, further affecting the system’s disinfection abilities.

Ultraviolet Light Intensity

Most UV water treatment systems have a UV dose delivery of about 30 mJ/cm². This UV intensity is strong enough to kill microorganisms like bacteria, viruses, and protozoans.

The intensity of the UV light affects the system’s water disinfection capabilities. Over time, as the lamp’s mercury vapor dissipates, the UV dose may decrease to a level that’s unable to kill viruses, bacteria, and other microorganisms. That’s why the UV lamp needs to be replaced periodically.

Uv lamp on table

Available Power Supply

Traditional UV water purifiers rely on a source of electricity to power the UV lamp and provide a continuous flow of treated water. If a UV system is left without power, whether due to a power cut or any other reason, the bulb won’t work – and the system won’t kill pathogens like bacteria.

📖 How to Ensure that UV Technology Kills Bacteria

UV disinfection systems are designed to target microorganisms like bacteria. If you want to ensure your UV system is working as effectively as possible, there are a few things you can do:

Replace the Bulb On Time

UV lamps have a lifespan of about 375 days, or 9,000 hours. Once a UV bulb reaches the end of its lifespan, its intensity will drop considerably. The result? Your water isn’t treated properly, and bacteria remains.

To keep your UV unit in good working order, replace the UV lights frequently.

Replacing a uv lamp in a uv water purification system

Clean the Sleeve Regularly

Over time, as water flows through the UV system, the glass quartz sleeve that surrounds the UV lamp accumulates dirt, sediment, and limescale. This buildup of organic matter clouds the glass, affecting the ability of the ultraviolet rays to penetrate the water. As a result, some bacteria could remain as the water passes through the chamber.

The best way to prevent this from happening is to clean the sleeve once a year, and replace it after three years.

Install a Pre-Filter

Water that’s sediment-rich affects the UV disinfection process. Most manufacturers advise you to install a sediment pre-filter that’s specifically designed to remove large particles from untreated water before it reaches the UV light. A 5-micron sediment filter is the best filter to install upstream of an ultraviolet system.

The added bonus of installing a pre-filter is that it doesn’t only protect the UV system from contaminants like sediment and heavy metals; it also protects you. Many people combine a UV filter with several other water filters that can remove dangerous chemicals, lead, VOCs, and more.

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📝 Takeaway

So, does ultraviolet technology kill the likes of bacteria in drinking water? Yes, technically. However, the effectiveness of this method of purification depends on several factors, including the quality of your water, the age of the lamp, and the intensity of the light.

Luckily, you can keep a UVC system in good working order by cleaning the sleeve at least once a year, and changing the lamp as advised by the manufacturer. UV is one of the best means of protection against harmful microorganisms like bacteria – but, like all water treatment systems, this method only works if you’re prepared to fulfill your maintenance duties.

  • Jennifer Byrd
    Water Treatment Specialist

    For 20+ years, Jennifer has championed clean water. From navigating operations to leading sales, she's tackled diverse industry challenges. Now, at Redbird Water, she crafts personalized solutions for homes, businesses, and factories. A past Chamber President and industry advocate, Jennifer leverages her expertise in cutting-edge filtration and custom design to transform water concerns into crystal-clear solutions.

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