UV to kill germs in drinking water?

RapidEye rapideye at usa.pipeline.com
Sat Jun 15 22:25:18 EST 1996

UV does not penetrate well in water; however, it will penetrate several
inches with no problems.  This means that if you are directing the light in
a section of piping less than 5 or 6 inches in diameter (depending on the
power of the light) it will help "sanitize" the water.  This used to be,
and still is a common practice with some pharmaceutical companies for
treating USP water systems.  I have worked with several systems with a UV
light inline after a series of water purification resin beds, and while
they did help reduce the bioburden, they never performed as advertised. 
Keeping in mind that this is after all chlorine, chloramines, and any other
biocidal chemicals have been removed from the water by purification - they
were very dependant on the flow rate through the piping.  The higher the
rate of flow, the faster the linear velocity through the relatively small
section of exposure to UV, the lesser the kill.  I has been my experience
that if the water chlorination procedure is appropriate and intact, UV
treatment of tap water is not really needed.  This may not be true for some
"exotic bugs", but if they are tough enough to withstand chlorination, an
extremely brief (and I do mean brief - less than a second in most single
pass systems) exposure to UV would probably not do much.  I would suspect
that for the price they are asking for a UV system, you could buy quite a
few 0.22 micron sterilization grade filters and sterile filter your
drinking water for less, with a much higher level of bioburden reduction.

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