[This article, written by the American Ground Water Trust was originally published in THE AMERICAN WELL OWNER, 1999, Number 4]


All visible light has a "color" or wavelength. We have learned about the colors of the rainbow since kindergarten! Ultraviolet (UV) light is a form of radiation that is not visible to the human eye. The light (irradiation) from UV lamps can be used to kill microorganisms and UV water treatment systems are relatively inexpensive and easy to install.

Ideally homeowners with wells will have water free from organisms. However, having a water treatment system for microorganisms adds an extra level of security.

It is essential that any water treatment system designed to protect against microorganisms is properly installed and maintained. UV systems are generally trouble free and low maintenance, but they need to be checked and serviced. To be confident, a “fail-safe” system can be installed so that if the UV system stops operating the water system shuts off.

UV radiation works as a drinking water disinfectant by altering the cellular material (DNA) in most microorganisms (viruses, bacteria, and protozoa) so that they cannot reproduce and cause infection. UV treatment systems produce light (radiation) over a narrow range of wavelengths known to "zap" most types of microorganisms.

UV systems may use "low-pressure" or "medium-pressure" mercury vapor lamps. In order to kill microorganisms the water must be exposed long enough for the UV light to do its work. For this reason UV treatment is an appropriate technology for residences because most home water needs are only for flow rates of a few gallons per minute.

An advantage of UV systems over chlorination is that no chemicals are added to the water and UV treatment does not cause the formation of any known toxic byproducts. However, UV treatment provides no residual germicidal protection. It is important that the UV system function within the manufacturer's design specifications to maintain the proper UV irradiation dose level that will ensure that microorganisms are fully irradiated (inactivated).

An UV water treatment system is relatively simple in design. Source water flows into a closed chamber with an UV lamp in the center of the chamber. The flow rate through the chamber must allow all the water to be exposed to the UV light. High turbidity in water can block light or hide microbes, and dissolved substances such as iron, manganese, organic carbon, and nitrates will increase the absorbance of the UV radiation by the source water, thus reducing the delivered UV dose. Pretreatment to reduce the concentration of these compounds may be necessary to optimize the performance of the UV system.

Installing an UV treatment system, or any other water disinfection system is not a substitute for proper well design and construction. If you have a dug well as a supply source, replacing the well is probably a more satisfactory long-term option. If a dug well or spring is your only supply option then look at all the treatment options before you decide what to do. Make sure you get advice from an expert!

[© American Ground Water Trust. This article may be reprinted for non-commercial educational purposes provided it is used in its entirety and that reference is made to its source as an article in THE AMERICAN WELL OWNER, 1999, Number 4]