The City of Henderson, Nevada has pioneered the use of ultraviolet (UV) light technology for disinfecting municipal water to combat pathogens such as cryptosporidium and giardia. This innovative method has led to the establishment of standard procedures for UV water treatment facilities in the U.S., and Henderson's strategy serves as a model for new treatment facilities nationwide. The successful application of UV disinfection marks a significant advancement in public health water treatment, emphasizing the importance of clean drinking water.

1. The Ultra Violet Light Project in Henderson, Nevada:
Reducing Public Health Infection through the City’s Municipal Water Supply
John Whitehill, Jr., MPH, Tim Kelley, Jeremy Lustig, PE
Nevada State Health Division; City of Henderson, Nevada
Abstract
Methods
Conclusion
Objectives
References
City of Henderson Water Authority Facility
• Why UV?
• The mechanism of disinfection by UV light differs considerably from
chemical disinfectants such as ozone and chlorine. Chemical disinfectants
inactivate microorganisms by destroying or damaging cellular structures,
interfering with metabolism, and hindering biosynthesis and growth
(Snowball and Hornsey, 1998). UV light inactivates microorganisms by
destroying their nucleic acid, thereby preventing the microorganism from
replicating.
• New procedure in United States lead to development of a standard conformance
procedure for any UV water treatment and facility.
Munakata N., M Daito, and K Hieda. (1991). Inactivation spectra of Bacillus
Subtilis spores in extended ultraviolet wavelengths (50-300nm) obtained with
Synchrotron radiation. Photochemistry and Photobiology 54, pp761-768.
Snowball MR, and IS Hornsey. (1988). Purification of water supplies using
ultraviolet light. Developments in food microbiology, edited by RK Robinson,
p171-191.
United States Environmental Protection Agency. (2003). Ultraviolet Disinfection
Guidance Manual. U.S. EPA Headquarters Library, Washington, DC.
The use of UV light to disinfect drinking water involves the generation of UV
light with the desired germicidal properties and the delivery of that light to
pathogens. UV light is in the region of the electromagnetic spectrum that lies
between x-rays and visible light (Figure 1). UV disinfection occurs due to the
germicidal action of UV-B and UV-C with microorganisms (Munakata et al., 1991).
UV light is generated by applying a voltage across a gas mixture, resulting in a
discharge of photons.
The City of Henderson UV lamps designed for water treatment use a gas
mixture containing mercury vapor. Mercury is an advantageous gas for UV
disinfection applications because it emits light in the germicidal wavelength range
for optimal exposure (US EPA, 2003). As UV light propagates from the source, it
interacts with materials through absorption – the transmission of light to other
forms of energy as it passes through a substance, reflection – the change in
direction of light propagation when it is deflected by a surface, refraction – the
change in the direction of light propagation as it passes from one medium to
another, and scattering – change in the direction of light propagation caused by
interaction with a particle (US EPA, 2003).
In 2002, the City of Henderson Water Authority Facility was the first water
treatment facility to apply ultraviolet technology to meet the LT2ESWTR rule and
treat potable water for the inactivation of cryptosporidium and giardia in the
United States. With emphasis in recent regulations on controlling
cryptosporidium, the number of UV disinfection facilities is expected to increase.
Before 2002, there was not a standard UV conformance procedure
developed for the inactivation of cryptosporidium and giardia. With the help of
Paul Swaim, now the President of the International Ultraviolet Association (IUVA),
and Dr. James Malloy of the IUVA, the City of Henderson was the first pilot site
for the development and use of this procedure.
The City of Henderson has been blazing new trails in terms of public health
water treatment for nearly a decade. Their pilot research at their facility has paved
the way for hundreds of newly opened treatment facilities utilizing this new
method and standardization of water treatment.
Community water treatment has been used for primary prevention method to
prevent illness, decrease dental caries through fluoridation, and provide clean drinking
water for decades. The City of Henderson, Nevada currently leads the nation on a
new innovative ultraviolet (UV) technology that has been applied to the municipal
water supply for advanced disinfection. UV disinfection is the process of using
ultraviolet light to alter cellular molecular components essential to cell function and
has been proven effective in eliminating harmful bacteria, viruses (specifically
cryptosporidium and giardia), spores and mold to permanently purify water. The first
UV disinfection system was developed in France and now there are over 2,000 UV
disinfection systems to treat drinking water in Europe. The City of Henderson
conducted a pilot study to test the UV technology in the United States. The City of
Henderson Water Authority Facility is now being modeled and replicated nationwide in
places like the Cedar Water Treatment Facility in Seattle, Washington.
Figure 1: Electromagnetic Ultraviolet Spectrum