Environmental Engineering Reference
In-Depth Information
2.4 Lessons from Disease Outbreaks
Drinking water disease outbreaks are the result of multiple failures within a water
system. The most common failures that allow outbreaks to occur are improper or
neglected treatment and failure to monitor operations. Outbreaks indicate the need
for continual vigilance and adequate monitoring in the drinking water production
and distribution, as well as continual testing of water quality to maintain adequate
quality standards. Outbreaks can be used to gain knowledge and understanding of
the techniques and methods that are most effective for providing safe drinking
water. Lessons can be learned nationally within countries as well as internationally
among countries, as shown here from Canada, the United States, and Europe.
Steven and Elizabeth Hrudey are able to make conclusions in their book, Safe
Drinking Water (
2004
), based on their summary of outbreaks from 1974 to 2002.
They conclude that the multi-barrier approach continues to be a requirement for a
safe drinking water system. Barriers in place at each stage within the system for the
source, treatment, distribution, monitoring, and response are all required to ensure
safe drinking water. Both human and nonhuman elements can cause failures
throughout the system. Continued emphasis on the multi-barrier approach is nec-
essary in order to detect and treat contamination at all stages before the water is
distributed to the consumer. This approach is still the most effective method to
provide safe drinking water.
The barrier of treatment is critical to the overall process. If an unknown con-
tamination occurs, the goal of treatment is to inactivate and/or remove the pathogen
before the water continues into the distribution system. Chlorine is the most
commonly used chemical disinfectant because of its cost-effectiveness. We know
that standard chlorine disinfection is effective against bacterial contaminations of
Campylobacter and E. coli, but ineffective against protozoan contaminations of
Cryptosporidium, Giardia, and Toxoplasma. Cryptosporidium is the most resistant,
but all three protozoa are able to surpass simple chlorine treatment, which has been
shown to cause numerous outbreaks. In the wilderness it may not be possible to
prevent contaminants from entering water sources, especially surface water, but the
barriers of
filtration and disinfection are critical in preventing the spread of con-
tamination that lead to outbreaks.
Hrudey and Hrudey also conclude that microbial pathogens are the primary
concern for drinking water safety. All the included outbreaks are caused by patho-
gens, thus indicating the longevity and persistence of the problem and their domi-
nance among contaminations. Pathogens threaten the safety of drinking water
because of the possibility of contamination anywhere throughout a water system and
their ability to surpass the treatment process. Pathogens originate from within human
and animal fecal matter. Sources deemed to be of high quality could become con-
taminated with such matter, especially surface water sources. Hrudey and Hrudey
emphasize the growing occurrence of Cryptosporidium since the 1990s up to the
Walkerton contamination in 2000. With its high resistance to chlorine, the most
commonly used method of treatment disinfection, the threat of Cryptosporidium
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