What is a UV Water Purifier and How Does It Work?

Posted by
John Woodard on June 23, 2023

UV water purifier treats micro-biologically unsafe water with germicidal ultraviolet light. The UV wavelength scrambles the DNA of living organisms in the water so that they can no longer reproduce and make you sick. If you drink bacteria-infested water, the organisms can embed in your digestive tract and replicate. Ultraviolet radiation renders bacteria, viruses, parasites, and fungi unable to replicate by damaging the nucleic acids of their DNA.

Ultraviolet Water Treatment Explained

  1. How a UV water purifier works
  2. Are UV purifiers safe?
  3. Are UV purifiers effective?
  4. UV water purifiers vs. water filters
  5. Advantages & disadvantages of UV purifiers
  6. When to use UV disinfection
  7. How to maintain your UV system

How a UV water purifier works

An ultraviolet (UV) water purifier exposes living organisms, such as bacteria, viruses, or cysts (like Cryptosporidium and Giardia) to a germicidal ultraviolet wavelength. With enough energy, UV radiation at the 254-nm wavelength disrupts the DNA in pathogenic microorganisms so they cannot reproduce. The ultraviolet light prevents bacteria from spreading disease through drinking water.

UV dosage is the measurement of energy (in mJ/cm²) delivered by a UV water purifier. The more dosage provided, the more energy delivered to treat contaminated water. This energy becomes sufficient at a certain threshold to inactivate most of the microorganisms in water.

What does a UV disinfection remove?

UV disinfection deactivates living organisms, such as bacteria, viruses, spores, and cysts, but it does not remove particles from water, add chemicals, or remove bad tastes and odors.

UV disinfection treats water for:

  • Cryptosporidium
  • Giardia
  • Dysentery bacilli
  • Salmonella
  • Mycobacterium tuberculosis
  • Streptococcus
  • coli
  • Hepatitis B
  • Cholera
  • Algae
  • Fungi
  • Some viruses

Several years ago, the city of Milwaukee flooded, and cryptosporidium infected the water supply. Cryptosporidium, also known as Crypto, is a parasite that enters the intestinal tract and causes illnesses such as Montezuma's revenge. Crypto is resistant to chlorine used to disinfect city water, and the water in Milwaukee resulted in hundreds of deaths. UV water purification protects you from pathogenic organisms that chlorine cannot kill, like cryptosporidium.

Learn more: How to remove bacteria from your water

What's inside a UV water purifier?

A UV water purifier includes a chamber that encases the quartz sleeve and UV lamp. The glass quartz sleeve holds the UV lamp that emits a germicidal wavelength of radiation (UV-C) to deactivate living organisms. The quartz glass sleeve is transparent to the UV wavelength, which allows UV light to penetrate the glass and disinfect the water. A quartz sleeve protects the UV lamp from the water because water and electricity do not mix well. One or two O-rings seal the whole system together.

UV lamp

UV lamps run on mercury vapor. The mercury vapor is loaded into a UV lamp in the form of little beads. The mercury vapor created from these beads power the lamp.  Occasionally, you may see beads rolling around in the lamp.  

Are UV water purifiers safe?

UV water treatment is safe. It does not use harmful chemicals or alter the composition of water. A UV sterilizer uses UV-C light to disinfect. UV-C light is harmful to humans just as it is for microscopic living organisms. However, you are not at risk of exposure unless you touch or look at the UV bulb while it is on.

Chlorine treatment is an alternative to UV, but ultraviolet treatment is much safer. Ultraviolet light treats water for protozoa that chlorine disinfection is unable to remove. A UV system is much easier to maintain and safer to use than chemical disinfectants. Treating water with chlorine requires a retention tank and precise injections and solutions. Many wastewater treatment plants now use UV water purification to eliminate harmful chemical by-products in water from chlorine or chloramine treatment.

Are UV water purifiers effective?

UV systems are effective at deactivating 99.99% of living organisms in water. They are designed to run constantly to guarantee the water you use is always safe. Because a UV purifier is not a filter, there is no wastewater or debris left behind to clean out. Every drop of water that enters the UV system is purified.

UV water purifiers vs. water filters

Unlike water filters, a UV water purifier does not remove particles from water. Reverse osmosis systemsultrafiltration systemscarbon filters, and ceramic filters all separate contaminants from water through tiny pores of a filter or a membrane. UV treatment purifies water by exposing living organisms to ultraviolet light, but it does not filter them out. Water filters do not remove bacteria and viruses with the same effectiveness as UV systems. UV disinfection works alongside water filtration systems to provide clean water.

Learn more about: Reverse osmosis systems | ultrafiltration systems | Activated carbon filters | Ceramic filters

Is UV necessary for a water filter?

UV purification is not necessary for a water filter, but a water filter is necessary prior to a UV system. UV systems are most effective when water is clear, so they must have at least a five-micron pre-filter to prevent living organisms from hiding behind loose particles. You could use a sediment filter to remove dirt and debris from a well water supply or a water softener to reduce iron as prefiltration. A UV purifier is the last thing water passes through on the way to the house.

Test your water quality before you use a UV system to make sure the water does not exceed these levels:

  • Hardness < 7 gpg (grains per gallon)
  • Iron < 0.3 ppm (parts per million)
  • Manganese < 0.05 ppm
  • Turbidity < 1 NTU (nephelometric turbidity units)
  • UVT < 75%
  • Tannins < 0.1 ppm

Advantages of a UV water purifier

UV water purifiers provide many benefits over chemical sterilization.

  • Deactivates bacteria and viruses. When subjected to ultraviolet light, bacteria and viruses are no longer able to reproduce.
  • Disinfects without chemicals. Ultraviolet wavelength does not leave the by-products in water that chemical disinfectants do.
  • Adds no tastes or odors. UV disinfection does not chemically alter the water in any way, shape, or form.
  • Easy to maintain. An annual UV lamp change is the most frequent maintenance need.
  • Does not waste water. The UV treatment process does not output any water to the drain.
  • Protects during natural disasters. When city water is compromised, a UV system keeps your drinking water safe.

bacteria in water

Disadvantages of a UV water purifier

Despite their many advantages, there are a few disadvantages to UV water purifiers compared to other disinfection methods.

  • Does not remove contaminants. UV only deactivates living organisms, so the system needs prefiltration to remove loose particles.
  • Heats the water. When you are not running water and it is sitting in the chamber, the UV lamp heats the water up.
  • Does not work during a power outage. A UV system requires electricity to run.
  • Does not work unless water is clear. Ensure that you have appropriate prefiltration installed before water reaches your UV system.

When to use a UV purifier

UV purification is the best option any time your water contains bacteria or if you want additional protection in the case of a natural disaster. By the time your city water plant issues a Boil Water Advisory, the water has already been contaminated. Having a UV system keeps your water free of harmful viruses and pathogens when the water supply is compromised.

If you own a private well or your water is stored in a storage tank, you will need a UV water purifier unless you disinfect your water with chemicals. The well owner is responsible for removing bacteria from water, and ultraviolet treatment is the most effective way to do it. A Rusco spin-down filter is an excellent prefilter for well water before UV disinfection.

UV water purifiers for your home

UV systems are POE (point-of-entry), which means you install them before water enters your home to purify the water throughout your house. Most of the time, typical household pressure is enough for a UV system to operate. However, a flow restrictor should be used to ensure water does not flow too quickly through the system. Water must be subjected to UV light for a specified time before it is disinfected. If the flow rate is too high, water flows through the UV system too quickly to be considered safe.

UV water purifiers come in a wide variety. The size UV system you need depends on the  flow rate of your water. Sizing according to flow rate allows water to contact the germicidal wavelength long enough to be effective. Like the size, the price of UV systems varies. Typically, a residential UV system costs around $400 or $500.

UV water purifiers for travel

Handheld UV water purifiers are perfect for backpacking, camping, or traveling around the world. The Steripen by Viqua sterilizes water in seconds without exposing you to UV rays. Handheld UV purifiers come as a single system or as a package with a sediment prefilter for water containing a lot of dirt and debris.

How to maintain your UV water treatment system

UV water purifiers last many years, but they require maintenance like any other water treatment system. However, UV systems are easy to maintain and designed to run continually.

  • Replace the UV lamp once a year. UV lamps use mercury vapor as fuel to ignite the UV wavelength. Over time, the mercury inside the lamp dissipates. A UV lamp lasts about 9,000 hours or 375 days (if you run it all the time).
  • Clean the quartz sleeve. The glass quartz sleeve that surrounds the lamp needs to be clean for the UV lamp to work effectively. Check the quartz sleeve when you change the lamp to make sure it is clean.
  • Replace the quartz sleeve once every two years. Quartz sleeves are very fragile, so keeping an extra on hand is recommended in case of an accident.

Learn more: How to maintain your UV system



If you have any additional questions, please do not hesitate to contact us.


Comments 1-4 of 4
Leave a comment