Ultraviolet (UV) systems are water disinfection systems used to clean water of live organisms that make people sick. Disinfecting water means cleaning it so it is safe to drink. Treating water with ultraviolet systems inactivates the harmful infectious microbes in the water. Unlike filtration systems, ultraviolet systems do not remove the organisms from the water; they render the organisms harmless by using UV radiation. Ultraviolet is a wavelength of light in a range that is invisible to the human eye.
Inactivating a parasite or microorganism means killing it so it is no longer harmful if consumed. The UV wavelengths that kill bacteria exist within a narrow sub-range of the ultraviolet wavelength. Not all wavelengths of ultraviolet light disinfect water. UV disinfecting technology can be more costly than other methods of disinfecting water, and has some drawbacks that require special precautions. Despite these problems, ultraviolet systems can be the best choice for disinfecting water in a remote location far from modern conveniences like electricity, running water, and roads, like those found in developing countries.
Types of tiny organisms in water that can be rendered harmless using ultraviolet systems include giardia bacteria, salmonella bacteria, and the shigella bacteria, which causes cholera. This type of organism is called a microorganism, but it can also be called a microbe. A microorganism cannot be seen by people without the aid of a microscope. The smaller the microorganism that needs to be inactivated, the longer exposure to UV radiation is needed to kill it. Likewise, larger parasites generally need less UV treatment to inactivate them.
Ultraviolet systems are as effective as disinfecting water through a boiling treatment but more expensive to use. In the field, UV disinfection can be more cost-effective despite the cost because of the labor, danger, and equipment necessary to treat a large amount of water by boiling it. Systems that disinfect using UV radiation can be more portable than the equipment required to boil a large volume of water.
Though UV radiation is effective in inactivating harmful microbes, ultraviolet systems most effectively disinfect water that has been prepared for treatment by softening and filtering the water for particles. Filtering water first makes ultraviolet systems more effective because it removes bacteria that might be trapped inside particles that protect the bacteria from the ultraviolet treatment. Usually, UV disinfecting systems are used along with reverse-osmosis filtration systems to achieve the best disinfecting results from the UV treatment.