Environmental Engineering Reference
In-Depth Information
as a river may change along its course. Designation of a water according to
best usage as a source of drinking water may imply high raw water quality but
does not preclude the need for proper treatment of the water before release to
consumers. Even then, faults in the water distribution system can permit access
of disease-producing microbes to an otherwise-adequately treated water. Further-
more, drinking water sources and subsequent purification steps vary widely in
quality among world nations. It cannot be assumed that water drawn from a
faucet is totally safe to consume, especially, in lesser-developed countries and
rural areas. During a visit to Canada in 1989, then-Czechoslovakian president
Vaclav Havel remarked, “I was surprised to learn that I was drinking tap water.
No one in Czechoslovakia would do that.”
1
Only about 2.6 percent of the global content of water constitutes fresh water
(atmospheric, and both surface and subsurface water bodies). Distribution of
fresh-water supplies among countries of the world is uneven and without regard
to population demands. Although water is a renewable resource, loss of usable
drinking-water supplies through unfavorable natural and manmade environmental
changes intensifies the challenge of providing adequate and safe drinking water
worldwide in the coming years. There is the anticipation of major alterations in
rainfall patterns and increased frequency of catastrophic floods owing to climate
change, meteoric expansion of human populations, and the likelihood of increas-
ingly unfavorable air, soil, and water quality in populous nations such as China
and India, where the focus is on competitive economic development. Compro-
mising environmental standards, especially with respect to drinking-water quality,
heightens the potential for transmission of disease-producing agents within the
population. Poor sanitation is unequivocally linked to the occurrence of high rates
of communicable and noncommunicable diseases worldwide.
The title of this chapter is “Disease Transmission by Contaminated Water.”
The classical concept of disease transmission by contaminated water is by the
oral route. Other avenues of infection are possible, however. Gleeson and Gray
2
have denoted four categories of infectious behavior in humans through contact
with contaminated water or lack of water:
1.
Waterborne disease
. Sickness or ailment results from ingestion of water
that is harboring a pathogen.
2.
Water-washed disease
. Sickness or ailment is spread by the fecal-oral route
or person-to person contact and facilitated by the lack of adequate water
for personal hygiene,
3.
Water-based infection
. Sickness or ailment is caused by infection arising
through ingestion of a pathogenic agent (e.g., guinea worm larvae) or inva-
sion of the body through water contact (e.g., schistosome and other trema-
tode larvae able to penetrate the skin of individuals in contact with water).
4.
Water-related diseases
. Sickness or ailment is facilitated by insect vectors
that breed in waters (e.g., malaria mosquitoes and filariasis arthropods that
carry viruses responsible for dengue ad yellow fever).
