An ultraviolet water purifier uses ultraviolet light to destroy bacteria, fungi, and parasites that can make people sick. They can be useful for travelers or campers who have drunk water that comes from an unreliable municipal system or from a possibly contaminated source like a river or lake. UV water purifiers can also be used to sanitize home water supplies where the water comes from a well or where residents are particularly susceptible to infectious disease.
Ultraviolet water purifiers are effective against waterborne pathogens such as E. coli, salmonella, giardia, and dysentery. Most municipal systems use chlorine to kill these microorganisms, but if a home’s water comes from a well or if a traveler is in a country where municipal water treatment is inconsistent or non-existent, water can be contaminated with human and animal feces from sewage systems or from storm runoff, or from dead animals upstream or in reservoirs.
The radiation in an ultraviolet water purifier works by destroying the replication capabilities of the microorganisms’ DNA. The microorganism is unlikely to make a person ill if it cannot reproduce inside the body. Water that has been purified with a UV light must be stored in a dark place, however, because exposure to light can reactivate the DNA’s ability to reproduce. UV water purification is often considered preferable to chemical purification with chlorine or iodine because the taste of the water is not altered, and an ultraviolet water purifier does not affect the water’s mineral content.
To destroy harmful pathogens, an ultraviolet water purifier exposes the water to around 245 nanometers of ultraviolet radiation from a mercury low-pressure lamp. In a home system, the lamp is housed in a quartz sleeve that the water takes several second to pass through, which is enough time to neutralize disease-causing microorganisms. In portable models for campers and travelers, the light is slightly larger than a pen and is directly inserted into a container of water and held there for several minutes.
For an ultraviolet water purifier to be most effective, the water must be very clear so the particles do not shade the pathogens from the light. Additionally, some microorganisms, such as the protozoan parasite that causes giardia, are large and hard-shelled which can make the radiation ineffective against them. For these reasons, UV water purifiers are most effective when used with ceramic filters that physically block sediment and large microbes before the water is radiated.
