UV water treatment?

[SGT Rock]

I was reading that article about Giardias and one thing it mentioned was how water close to the surface was safer because the UV from the sun killed the critters in it. So I got to thinking what if you just pot water in a clear bottle and let it sit in the sun. Anyone out there with a better education have an opinion about this?

[Tha Wookie]

I don;t know any research on this, but my guess is that it would depend on the length of time. The protein shell around the giardia protozoa is an adequately developed defense system, that might need a very long exposure if it were possible to kill it with solar filtration. I would guess it would longer than you would want to carry it. Even streams in high-sunlight areas, such as Scissors Crossing on the PCT, have been found to harbor giardia. Interesting thought. Maybe there is some research on it somewhere....

[Footslogger]

I don't know for sure either (never actually tried it) but years ago I did some research/reading about water purification methods and UV exposure was right up there near the top of the list. From my memory though ...simple exposure to sunlight (UV) took a relatively long time in order to be effective and the recommendation was to use a shallow container with a large opening/surface area.

'Slogger

[dougmeredith]

I don't know the answer to the original question, but I do have a related curiosity. The disinfection tablets (chlorine) I have say to add them to the water and then keep the water OUT of direct sunlight while they work. Of course it doesn't say why. I always thought this was strange. It seemed to me that, if anything, the UV would help the process along. Maybe UV deactivates the chlorine compound somehow.

Doug

[rhjanes]

yes, clorine looses it's effectiveness in the sun. I used to work pools. On sunny days, even with no one using the pool, they would require more clorine to keep the health department happy. Acid also changes how clorine works. Lower PH helps the clorine to do it's job over a longer period of time.:jump

[Youngblood]

I was reading that article about Giardias and one thing it mentioned was how water close to the surface was safer because the UV from the sun killed the critters in it. So I got to thinking what if you just pot water in a clear bottle and let it sit in the sun. Anyone out there with a better education have an opinion about this?
I vaguely recall reading where they where putting water in plastic soda bottles and putting them on roofs to kill the nasties with sunlight in some impoverished area.

If I can't get spring water I prefer places where it has some sun exposure and some aeration... I think UV and oxygen are suppose to help.

[SGT Rock]

I vaguely recall reading where they where putting water in plastic soda bottles and putting them on roofs to kill the nasties with sunlight in some impoverished area.

If I can't get spring water I prefer places where it has some sun exposure and some aeration... I think UV and oxygen are suppose to help.
Thanks Youngblood, with that info I did a Google search and found this:



A very low-tech method, using direct solar radiation to reduce pathogens, was field-tested by researchers from the Royal College of Surgeons in Dublin, Ireland. The researchers gave 206 Masai children clear, 1.5-liter plastic bottles. The children in the test group were told to fill the bottles (from the contaminated water supply) and place them on the roof, from dawn to midday. The control group kept their bottles inside. Diarrhea incidence in the two groups was tracked over 12 weeks. The researchers found that this solar radiation method may significantly reduce diarrheal disease for communities that have no other way to disinfect water (4).

4. Conroy, R.M., M. Elmore-Meegan, T. Joyce, KG. McGuigan, and J. Barnes (1996), "Solar Disinfection of Drinking Water and Diarrhoea in Maasai Children: A Controlled Field Trial," Lancet, 348(9043): 1695.
How Stuff Works:Sun and water: an overview of solar water treatment devices. Retreived 9 August 2005 from http://home.howstuffworks.com/framed.htm?parent=question358.htm&url=http://solarcooking.org/sunandwater.htm

[SGT Rock]

Another search based on the previous search results found this:


"Solar disinfection is an effective water treatment method [...], especially when no chemical disinfectants are available. Ultra-violet rays from the sun are used to inactivate pathogens present in water. This technique involves exposing water in clear plastic bottles to sunlight for a day, for example on the roof of a house. In emergencies, empty bottles can be used that are left over from an initial shipment of drinking water. Bottles need to be cleaned, filled to three quarters and shaken thoroughly 20 times, before being filled completely. The bottles are then exposed to sunlight for 6 hours (or for 2 days if the sun is obscured by clouds). The water should be consumed directly from the bottle or transferred in a clean glass for drinking. To be effective, solar disinfection must be applied to relatively clear water. For further information, see annex [...] and http://www.who.int/water_sanitation_health/dwq/wsh0207/en/ (http://www.who.int/water_sanitation_health/dwq/wsh0207/en/)."
Abstract taken from the International Network to Promote Household Water Treatment and Safe Storage (http://www.who.int/household_water/en/) (managed by WHO) - - to which they have just added a special fact sheet on emergencies (http://www.who.int/entity/household_water/resources/en/emergencies.pdf) IRC: Solar disinfection (sodis). Retrieved 9 August 2005 from http://www.irc.nl/page/16714

So that sort of supports what Wookie said.

[justusryans]

Thats hot a steripen works, uv kills all the buggers