Ultraviolet (A) light kills nearly all pathogens. The duration and intensity of exposure to achieve purification varies.

"A number of factors combine to make ultraviolet radiation a superior means of water purification for rainwater harvesting systems. Ultraviolet radiation is capable of destroying [UV does not actually destroy, but inactivate bacteria, see note] all types of bacteria. Additionally, ultraviolet radiation disinfects rapidly without the use of heat or chemical additives which may undesirably alter the composition of water.

The most familiar part of the spectrum is a narrow band of wavelengths visible to the human eye. Another band with wavelengths shorter than those of visible light, and not visible to the eye, is the ultraviolet part of the spectrum. Ultraviolet radiation can cause changes in living matter. The sun's rays cause sunburn. Rays from a welder's torch burn the unprotected eyes of an observer. The ultraviolet spectrum includes wavelengths from 2000 to 3900 Angstrom units (Å). One unit is one ten billionth of a meter. The 2000 to 3900 Å range may be divided into three segments:Long-wave ultraviolet - The wavelength range is 3250 to 3900 Å. These rays occur naturally in sunlight. They have little germicidal value. Middle-wave ultraviolet - The wavelength range is 2950 to 3250 Å, also found in sunlight. Middle-wave UV is best known for its sun-tanning effect; it provides some germicidal action, with sufficient exposure. Short-wave ultraviolet - The wavelength range is 2000 to 2950 Å. This segment possesses by far the greatest germicidal effectiveness of all ultraviolet wavelengths. It is employed extensively to destroy bacteria, virus, mold, spores, etc., both air- and water-borne." 1

There are many manufacturers of UV water sterilizers. They vary is size for virtually every application.

Good Gadgets

One of the most popular manufacturers of UV sterilizers for survival, camping, and hiking is Steri-Pen

SOlar water DISinfection (SODIS)

UV light from our sun, Sol, is free and ample.

"SOlar water DISinfection (SODIS) involves filling clean PETE (Polyethylene Terephtalate) 2 transparent plastic bottles with water and exposing them to full sunlight for six or more hours. [JWR Adds: Do not use polycarbonate water bottles, such as those made up until recently by Nalgene, since that type of plastic blocks ultraviolet (UV) light!] The combination of UV-A radiation and raised water temperature disinfects the water. There are a few drawbacks to this method. SODIS efficiency depends on the physical condition of the plastic bottles, with scratches reducing the efficiency of the SODIS process. There has been some concern over the question whether plastic drinking containers can release chemicals or toxic components into water, a process possibly accelerated by heat. A solar cooker will make the SODIS process more efficient." 3

Using a convenient window sill, one can stack up bottles of water. If using city water, capping the bottle immediately preserves a small amount of free chlorine as an additional measure of purification. Being in a window sill the water is exposed to UV for extended periods of time maintaining the water purity. This water bank pictured has 13.5 days of water at the time the picture was taken.





by: Zee-Man



1 Everything You Need to Know about Ultraviolet Water Purification by John Mone - http://www.harvesth2o.com/uv.shtml2 View the ZSDW page on Water Containment for details about PETE plastic for safe handling practices.3 SurvivalBlog - http://www.survivalblog.com/2009/02/solar_water_disinfection_and_p.html