Estimating the public health risk associated with drinking water in New Zealand : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Massey University, New Zealand
This thesis is concerned with the application of both epidemiological and molecular tools
to assess the drinking water safety in New Zealand. Compromised drinking water safety is
commonly manifested as gastrointestinal illness. The studies in this thesis were motivated
by the desire to nd ways of reducing the burden of such illness in the human population.
Although the studies were conducted in the New Zealand setting the methodologies can be
readily applied elsewhere.
The rst study investigated the factors associated with the presence of microbes in raw
water intended for public consumption. Random forest, an established non-parametric statistical
method, was used to model data with possible complex interactions and identi ed
variables that were predictive of the presence of microbes in raw drinking water. E. coli,
which is widely used as a microbial contamination indicator in the water industry, was found
to be a better predictor of the presence/absence of Campylobacter (bacteria) than protozoan
microbes (Cryptosporidium and Giardia). This suggests that alternative methods of
determining the presence/absence of pathogens in water should be developed. In the second
study, the relationship between river
ow and reports of cases of gastrointestinal illness was
described using the distributed lag modelling approach. This revealed a positive relationship
that peaked around 10 days after high
ow. Further, the river
illness relationship was stronger in small drinking distribution networks than in large ones.
The small drinking water distribution networks could be targetted for facility upgrade in
order to enhance their ability to deliver microbiologically safer drinking water.
The third study utilised culture-dependent methods to assess the public health risk associated
with drinking water supplied at outdoor recreation facilities | campgrounds. Water
treatment using methods such as ultra violet and chemical treatment were found to be
highly bene cial for the campgrounds to deliver drinking water that was microbiologically
safe and compliant with water safety regulations. The pro les and functional factors of
drinking water microbial communities are described in the fourth study. Techniques from
the fast-growing eld of metagenomics were employed for this purpose. The capability of
metagenomic techniques to detect multiple pathogens in a single assay was demonstrated.
This has the potential to greatly enhance the speci city and sensitivity of microbial water