Civil Engineering Reference
In-Depth Information
CHAPTER 4
Microbiology of Drinking Water
INTRODUCTION
All natural waters support biological communities, which in turn contain microorgan-
isms. In almost all instances, a portion of the microorganism population will have
derived from mammalian species, and a small subgroup of these will represent poten-
tial health concern to humans.
The microbiology of drinking water is complex, and our understanding of it is far
from complete. Recent advances in our ability to isolate and identify microbes point
to an even broader range of human health threats than had been previously realized.
This chapter provides an overview of the state of knowledge on pathogens in raw and
treated water. It discusses the history of waterborne disease outbreaks in the United
States, reviews issues of groundwater contamination, and examines the potential for
further microbial regulations as relating to the question of emerging pathogens.
PATHOGENIC ORGANISMS
Although the epidemiological relation between water and disease had been suggested
as early as 1854, it was not until the establishment of the germ theory of disease by
Louis Pasteur in the mid-1880s that water as a carrier of disease-producing organisms
could be understood. In 1859, London experienced the ''Broad Street Well'' cholera
epidemic, and Dr. John Snow conducted his famous epidemiological study, as dis-
cussed in Chapter 1, ''Criteria and Standards for Improved Potable Water Quality.''
Now, more than 100 years later, the list of potential waterborne microbial diseases is
considerably larger, and includes bacterial, viral, and protozoan parasitic microorgan-
isms.
Bacteria
Bacteria are single-celled organisms ranging in size from 0.1 to 10
m. The physical
structure of the bacterial cell can be characterized by shape, components, size, and the
manner in which they grow. Most bacteria can be grouped by shape into four general
categories: spheroid, rod, curved rod or spiral, and filamentous.
Cocci,
or spherically
shaped bacteria, are approximately 1 to 3
m in diameter.
Bacilli,
or rod-shaped bac-
teria, are variable in size and range from 0.3 to 1.5
m in width (or diameter) and
from 1.0 to 10.0
m in length.
Vibrios,
or curved rod-shaped bacteria, typically vary
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