Environmental Engineering Reference
In-Depth Information
CHAPTER 1
DISEASE TRANSMISSION
BY CONTAMINATED WATER
RICHARD F. UNZ, EMERITUS Professor
The Pennsylvania State University, Department of Civil and Environmental
Engineering
INTRODUCTION
Water is traditionally viewed as the “universal solvent” which accounts for its
vital support of all living things. The property of solvency is also responsible, in
the main, for the chemical quality of natural water as pertains to the dissolution of
naturally occurring minerals, atmospheric gases, and organic molecules present
in plant and animal residues. Natural waters are also a vehicle for suspended
matter, including microbial cells.
Fresh surface waters are collectively represented by streams, rivers, lakes,
ponds, and reservoirs and constitute a major source of drinking water. Unless
protected, they are prone to receiving anthropogenic discharges of domestic,
industrial, and agricultural wastewaters. Such adulterations alter the natural water
quality, and the severity of change is dependent on the rate, extent, and com-
position of the waste discharges. Groundwater (subsurface water) is the most
plentiful form of available freshwater. However, owing to greater inaccessibility
and higher cost, groundwaters are less utilized as a water supply than surface
waters.
The consequences for utilizing polluted waters as a drinking water supply are
well documented historically and will be dealt with in the section “Historical
waterborne disease background.” Natural water should be valued both as a com-
modity and a habitat for aquatic life. The former consideration pertains to public
health issues and the latter deals with the ecological value of natural waters.
Surface waters can be rated according to best usage with respect to drinking,
bathing, shellfish rearing, fishing, and navigation purposes. A set of minimum
water-quality standards defines the best usage of a water body. Waters suitable
for drinking-water supplies, recreational bathing, and shellfish rearing are moni-
tored regularly for microbiological quality. The best usage of a water body such
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