Re: SB: alt Low cost water> uv sterilizer

["Scott Willing" <willing@mb.sympatico.ca>]

On 30 Aug 2002 at 11:07, Sherwood Botsford wrote:

> On Thursday 29 August 2002 02:14 pm, Charmaine R Taylor wrote:
> : A really low cost way to purify/sanitize water is to use a
> : glass jar, with metal lid- aka Mason jar- and solar cook
> : it...it does not have to boil to be safe, only 140 deg for a
> : few minutes. (  just 1 min I believe)...the
[snip]
 
> I disagree.  There are good reasons when sanitation alerts go out that
> the word is 'boil water for 10 minutes.'   Our dishwasher (school
> cafeteria) is required to cycle for 30 seconds at 185 F.

There is some contention here obviously, and I'm not qualified to 
offer expert comment, but I suspect the "boil water for 10 minutes" 
order is a typical, over-the-top, cover-yer-ass sort of directive 
issued by public officials who probably also own stock in energy 
companies. ;-)
 
> However if 140 degrees kills 90% of the common bugs, it may make a
> health difference.  It's certainly better than nothing.

Ditto above. Some sources claim this does the trick, period.
 
> A better way may be to get quartz jars.  There are commercial UV
> sterilizers that have a bright UV lamp and a quartz tube.  Both inside
> a mirrored tube.  The light is not enough to appreciably warm up the
> water, but kills six nines of the bugs (99.9999%)

And they are almost universally designed to run 24/7, so you better 
have the energy to devote to them. It may not seem like much, but 
anything in constant use adds up. Also the supply electronics for 
most of these units have a poor power factor, such that they use even 
more energy than they really should for a given tube rating (speaking 
as an off-grid guy with modest solar power system).
 
> I would think that this could be adapted to work with a trough 
> solar reflector, and pairs of buckets and some tubing and could
> provide clean water for a neighbor hood group of vilages.

A challenge with UV sterilization, whether via the sun or UV lamps, 
is that there is no residual bug killin' ability downstream of the 
sterilizer. Ideally you should draw your water as close as possible 
to it. I'm not poo-pooing the concept (au contraire) but 
recontamination is a real threat, and chlorine does have the 
advantage that it remains in the plumbing etc.

FWIW, a community in British Columbia, known for its great mountain 
water, and to which many people have moved *because* they have 
objections to (or known sensitivities to) chlorine, just won a 
landmark decision permitting them to install a community UV 
sterilization system. (Health authorities had been trying to force 
them into using full-time chlorination.) However, even they have 
always had and will continue to have a chlorinator ready to bring 
online to disinfect the distribution system in the event of a 
contamination problem downstream of the UV unit.

Interestingly, despite what an awesome poison chlorine is, it isn't 
effective against certain organisms such as cryptosporidium, which 
has caused some well-publicized public health problems in Canada in 
recent times. UV gets 'em, assuming the exposure (strength * time) is 
sufficient.

-=s

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