A 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 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
- How a UV water purifier works
- Are UV purifiers safe?
- Are UV purifiers effective?
- UV water purifiers vs. water filters
- Advantages & disadvantages of UV purifiers
- When to use UV disinfection
- How to maintain your UV system
How a UV water purifier works
A 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. At a certain threshold, this energy becomes sufficient enough to inactivate most of the microorganisms present in water.
What does a UV disinfection remove?
UV disinfection deactivates living organisms, but it does not remove particles from water, add chemicals, or remove bad tastes and odors.
UV disinfection treats water for:
- Dysentery bacilli
- Mycobacterium tuberculosis
- E. coli
- Hepatitis B
- Some viruses
Several years ago, the city of Milwaukee flooded, and cryptosporidium infected the water supply. Cryptosporidium is a parasite that enters the intestinal tract and causes illness like 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, like cryptosporidium, in water.
What's inside a UV water purifier?
A UV water purifier includes a chamber that encases the entire system. 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 don't mix well. One or two O-rings to seal the whole system together.
UV lamps run on mercury vapor. The mercury vapor is loaded into a UV lamp in the form of little beads. Occasionally, you may see beads rolling around in the lamp. These beads are mercury before it's vaporized to create fuel for the lamp.
Are UV 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. But unless you touch or look at the UV bulb while it's on, you're in no danger of exposure.
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 purifiers effective?
UV systems sterilize water quickly and effectively. UV disinfection deactivates 99.99% of living organisms in the 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's 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
Reverse osmosis systems, ultrafiltration systems, carbon filters, and ceramic filters all separate contaminants from water through tiny pores of a filter or a membrane. Unlike water filters, a UV water purifier does not remove particles from water. 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 as well as a UV system. UV disinfection works alongside water filtration systems to provide clean water.
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
- Disinfects without chemicals. Ultraviolet wavelength doesn't leave by-products in water like chemical disinfectants.
- 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.
- No water wasted. The UV treatment process requires no water to the drain.
- Protection during natural disasters. When city water is compromised, a UV system keeps your drinking water safe.
Disadvantages of a UV water purifier
- Does not remove contaminants. UV only deactivates living organisms, so the system needs prefiltration to remove loose particles.
- Heats the water. When you're not running water and it's sitting in the chamber, the UV lamp heats the water up.
- Doesn't work during a power outage. A UV system requires electricity to run.
When to use a UV purifier
UV purification is the best option any time your water contains bacteria or 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'll 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.
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's clean.
Replace the quartz sleeve once every two years. It's a good idea to have an extra sleeve on hand because they're fragile.