Waterborne Disease Outbreaks and the Multi-barrier Approach to Protecting Drinking Water - Global Drinking Water Management and Conservation - page 12

the multi-barrier approach to detect and treat the contaminant before it reaches the
consumer. A failure in one or more of the barriers can lead to the spread of
contamination, which results in an outbreak if not detected in the remainder of the
system. Most outbreaks in the history of drinking water contamination have been a
result of barrier failures. Failures can occur anywhere within the system, including
source water, operations, treatment, and distribution. Outbreaks are an indicator of
weaknesses within a water system. The number of outbreaks and their severity
re

ect poorly on the ability of an overall system to provide safe drinking water.
Also, the weather frequently plays a key role in outbreaks by introducing con-
taminants into water sources, often by runoff from either a heavy rainfall or spring
melt. Surface water is particularly vulnerable to weather occurrences because it is
easily accessible, in contrast to groundwater sources that have natural filtration.

through the soil, and therefore incur less contamination than surface water, in
general. Over time, with the knowledge gained through the experience of past
outbreaks, fewer outbreaks would be expected to occur as water systems improve to
prevent future contamination. However, this has not been the case, as contamina-
tion continues to be a major concern throughout the world, and surprisingly even in
developed countries such as Canada, the United States, and Europe.
This chapter is organized as follows: Protozoa contaminants of Cryptosporidi-
um, Giardia, and Toxoplasma are discussed

first. This is followed by a discussion
of bacterial contaminants of Campylobacter, and E. coli. For each contaminant a
description is included as well as the predominant outbreaks that each has caused.
Furthermore, a number of principles of watershed management are reviewed in
Sect. 5 .

2.2 Protozoa

2.2.1 Cryptosporidium

Cryptosporidium is a frequent microbial cause of drinking water outbreaks. This is
because as a protozoan it is resistant to chlorine disinfection, which allows it to
spread undetected throughout the distribution system to the consumer. Chemical
disinfection is a critical barrier in the multi-barrier approach to prevent the possible
spread of contamination, but alternative treatment is necessary for systems to be
effective against Cryptosporidium. Alternative treatments including coagulation,
sedimentation, filtration, ozone and ultra-violet light treatment have been deter-

mined to be effective against Cryptosporidium (Rose 1997 , p. 149). Communities
that rely solely on chlorine are the most vulnerable to an outbreak of cryptospo-
ridiosis, the disease caused by Cryptosporidium. Severe diarrhoea is the main
symptom of cryptosporidiosis. The majority of the outbreaks are related to treat-
ment failures within the water system, often a heavy reliance on chlorine and a
failure to provide filtration. Filtration is extremely important in removing Cryp-

tosporidium, particularly in communities that rely on surface water sources. This is