Ultraviolet (UV) systems expose water to the light from a special lamp. The light is at a specific wavelength capable of killing common bacteria. The percentage of organisms killed depends on the intensity of the UV light, the contact time that the water has with the light, and the amount of suspended solid particles in the water. The system adds nothing to the water, produces no tastes or odors, and typically requires only a few seconds of exposure to be effective. No residual is produced because UV radiation quickly dissipates into water. Therefore, treatment of the water occurs as the water passes into the light. !e light penetration into water is shallow, usually only two to three inches.
Suspended solid particles in the water can shield organisms from the light. Therefore, UV devices are often combined with other technologies such as particle filters, carbon filters, ion exchange units, and reverse osmosis systems to remove particles prior to UV disinfection. UV is often the last device in the “treatment train” (a series of treatment devices) following reverse osmosis, water softening, or filtration. The UV unit can either be a point-of-entry system, treating all the water entering the house, or a point-of-use device, treating water from a single tap, as a final disinfection method.
The typical UV treatment device consists of a cylindrical chamber housing the UV bulb along its central axis. A quartz glass sleeve encases the bulb; water flow is parallel to the bulb which requires electrical power. A flow control device prevents the water from passing too quickly past the bulb, assuring appropriate radiation contact time with the flowing water. It has been reported that turbulent (agitated) water flow provides more complete exposure of the organism to UV radiation.
Regardless of the quality of the equipment purchased, it will not perform satisfactorily unless maintained in accordance with the manufacturer’s recommendations for maintenance, cleaning, and part replacement. Keep a logbook to record equipment maintenance and repairs.
Since UV radiation must reach the bacteria to kill them, the housing for the light source must be kept clean. Commercial products are available for rinsing the unit to remove any film on the light source. An overnight cleaning with a solution of 0.15 percent sodium hydrosulfite or citric acid effectively removes such films. Some units have wipers to aid the cleaning process. Consider purchasing a unit with manual wipers to aid the cleaning process.
UV systems are designed for continuous operation and should be shut down only if treatment is not needed for several days. The lamp needs a few minutes to warm-up before the system is used again following shutdown. In addition, the plumbing system of the house should be thoroughly flushed following a period of no use. Whenever the system is serviced, the entire plumbing system should be disinfected with a chemical such as chlorine prior to relying on the UV system for disinfection.
UV lamps gradually lose effectiveness with use, so the lamp should be cleaned on a regular basis and replaced at least once a year. It is common for a new lamp to lose 20 percent of its intensity within the first 100 hours of operation, and that level is maintained for the next several thousand hours. Units equipped with properly calibrated UV emission detectors alert the owner when the light intensity falls below a certain level.
The treated water should be monitored for coliform bacteria on a monthly basis for at least the first six months of the device’s use. If these organisms are present in the treated water, the lamp intensity should be checked, and the entire plumbing system should be disinfected with a chemical such as chlorine.
Ensure the system you choose is installed and operated according to the manufacturer’s instructions. After installation, retest both the raw water (prior to treatment) and the treated water at a state certified laboratory to ensure it is working properly and removing the contaminants. You should continue to test the quality of both the untreated and treated water annually. This annual test will also help you determine how well your treatment system is working and whether maintenance or replacement of components may be necessary.
The following affect the disinfection efficiency of a UV system:
Before purchasing a water treatment device, have your water tested at a state certified laboratory to determine the contaminants present. This will help you determine if UV is an effective treatment method for your situation. See the fact sheet Questions to Ask When Purchasing Water Treatment Equipment for more information.
Consumers should inquire about the following before purchasing UV treatment:
NSF International is a non-profit organization that sets performance standards for water treatment devices. Because companies can make unsubstantiated statements regarding product effectiveness, the consumer must evaluate test results of the device to determine if claims are realistic. Products that have been tested or evaluated by NSF and meet their minimum requirements are entitled to display the NSF listing mark on the products and in advertising literature for products. Manufacturers and models that meet NSF’s standard are included in a listing published twice a year. For more information contact NSF at: 800-NSF-MARK (800-673-6275) or http://www.nsf.org/consumer-resources
Center for Agriculture Food and the Environment
This fact sheet is one in a series on drinking water wells, testing, protection, common contaminants, and home water treatment methods available on-line
and Cape Cod Cooperative Extension: 508-375-6699
http://www.capecodextension.org
MA Dept. of Environmental Protection, Division of Environmental Analysis
Offers assistance, information on testing and state certified laboratories: 617-292-5770
For a listing of MassDEP certified private laboratories in Massachusetts
U.S. Environmental Protection Agency, New England Office
Information and Education on where drinking water comes from; drinking water testing and national laws; and how to prevent contamination
US Environmental Protection Agency
For a complete list of primary and secondary drinking water standards
MA Department of Conservation and Recreation, Division of Water Supply Protection
Maintains listing of registered well drillers, information on well location and construction: 617-626-1409,
NSF International
The NSF International has tested and certified treatment systems since 1965. For information on water treatment systems: 800-NSF-MARK
Water Quality Association
The Water Quality Association is a not-for-profit international trade association representing the household, commercial, industrial, and small community water treatment industry.
Ultraviolet (UV) light was first discovered in the mid-20th century, introducing a new way for people to eliminate viruses and bacteria. Although UV technology has risen to prominence in recent years, especially during the current COVID-19 pandemic, the majority of the general public does not fully understand exactly how UV lighting helps kill viruses and bacteria. The following article will shed light (pun intended) on how UV light works, what UV-C products and equipment are available on the market, and the precautions that need to be taken to avoid exposure to human skin.
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UV light is divided into several ranges: UV-A, UV-B, UV-C (close to the visible light range) and Vacuum-UV (close to the x-ray range). The UV-C light range is the only one able to destroy germs. It is found in UV water purifiers, used in fish tanks, and in portable UV light sanitizers designed to destroy germs that may exist on your tech gadgets and other regular household items. UV-C light can fracture the molecular bonds of the viruses’ and bacteria’s DNA, affecting their ability to reproduce and ultimately killing them.
UV light is one of the seven sections that make up the electromagnetic spectrum. Lower frequencies are radio waves, microwaves, and infrared (IR). These are harmless to humans and animals. A mid-range frequency that many are familiar with is visible light. Ultraviolet (UV), X-rays, and gamma-rays are the highest frequencies and can be very harmful to humans if used without implementing appropriate safety measures.
As mentioned above, the 3 major types of UV radiation are UV-A, UV-B, and UV-C. UV-C rays can effectively eliminate bacteria and viruses as they have the shortest wavelength of the 3 major UV rays. Their short wavelength of 200 - 400 nanometers (nm) means that they have the highest energy, allowing them to kill deadly pathogens. How does UV radiation primarily kill microbes? UV-C light fractures the molecular bonds of the viruses and damages the DNA of microbes and bacteria, affecting their ability to reproduce and ultimately killing them. It has also been known to destroy “superbugs”, whose resistance to antibiotics makes them notoriously hard to eliminate. The efficacy of UV-C lighting has seen many people look to it as a means to kill the coronavirus by decontaminating surfaces and objects on which the virus may be present.
Studies conducted by researchers at John Hopkins University using UV light on “high touch” public spaces in hospitals such as bed rails, tray tables, and vitals monitors have revealed that it only takes 15 minutes for these objects to be disinfected using UV light. Remarkably, the study revealed 25 out of 27 high-touch surfaces used in the study were devoid of any bacteria after being exposed to UV light. To destroy bacteria, ultraviolet radiation is used as a disinfectant by utilizing a 200 to 300 nanometre range. To eradicate a virus, extremely high levels of UV light would be required and the amount of UV required and the time needed would be dependent on many factors, such as the shape and type of material that the virus is found on. Current UV devices are insufficient to adequately kill viruses. Efforts are being made to create a portable UV device that is capable of releasing high-intensity rays able to kill viruses, such as the SARS-CoV-2 virus.
UV-C lights are available to consumers in a variety of different products including UV-C lamps and wands. The length of time needed to destroy viruses and bacteria is unique to each device. Each UV-C device will state on the packaging or the packaging insert how long it will take to sanitize the product and how close the object will need to be held to the device. UV light is only effective on smooth, flat surfaces and cannot effectively disinfect rounded objects such as the buttons of a remote control, nor can it get into crevices. Other forms of disinfection would be required to adequately clean these objects.
A virus’s exposure to radiation is believed to subdue cell-mediated immunity, which may affect the course of a viral infection. As previously mentioned, UV-C possesses the ability to critically destroy a virus’s molecular bonds, inhibiting the virus from multiplying and becoming a threat to humans. Sunlight, particularly UV radiation, is the main natural virucide that exists in our environment. UV radiation destroys viruses by chemically changing their genetic makeup. The most efficient wavelength to bring about inactivation is 260nm. The nucleic acids within viruses can be harmed by UV-A and UV-B radiation, however, they are not as effective and potent as UV-C.
The growing popularity of UV radiation has seen it being used in a variety of products such as UV germicidal lamps, and water filters. Recent developments have helped to place UV technology in portable wands that may be easily transported. Because of this, it is being used in a variety of environments, from hospitals to households. The large variety of objects that UV products can disinfect include, but are not limited to: surfaces, paper goods, water, air, toys, household objects, tech devices, and even fresh produce.
Not all UV-C products being advertised are genuine, therefore it is important to do sufficient research before committing to buying a specific product. Counterfeiters are looking to make a quick dollar at a time when UV-C product sales are soaring. Ensure that you have purchased your product from a reputable source. This can be done by checking the reviews of the product that you are intending to buy and doing a quick search of the company online to ensure their credibility.
The correct safety precautions must be taken when handling UV radiation, specifically UV-C as it is the strongest form of ultraviolet radiation. Overexposure to UV-C may cause sunburn or even skin cancer. After purchasing a UV-C product, make sure that it is installed and configured in a way that blocks exposure of the rays to any humans and animals. Stringent safety measures are particularly important as UV-C rays are invisible which increases the chance of accidental exposure. Materials and objects that may be present in the home and workplace such as houseplants, wood, and plastic may be damaged from accidental exposure to UV radiation.
UV radiation as a form of disinfection has been steadily growing in popularity. Its appeal lies in its efficacy when used correctly, and in the portability of the increasing number of UV-C products that are becoming available. Always remember to implement the correct safety measures as UV-C rays can be extremely harmful to humans, animals, and objects. UV radiation is an exciting technology that, if harnessed correctly, may make our world a safer and cleaner place.