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 The largest single use of antimicrobial agents
is the purification of drinking water. The disinfection of drinking water
was introduced in the United States in the early 1900s to eliminate disease-producing
contamination and unpleasant taste and odor, and it has substantially reduced
the deaths and disease due to cholera, hepatitis, and amoebic dysentery.
In areas where water is not adequately disinfected, outbreaks of these diseases
still occur.
The most common methods now used to disinfect
drinking water involve the use of free chlorine and chloramines (a mixture
of chlorine and ammonia). Roughly 90 percent of the drinking water in the
United States is disinfected with these compounds while about one percent
is disinfected through the use of ozone.
Chlorine
and chloramines are the antimicrobial agents used to provide more than 200
million people with disinfected drinking water. Disinfecting drinking water
at the treatment plant is a complicated process that can be done in a number
of ways. A few general steps apply for most treatment processes. In systems
that use chlorine gas, raw water is dosed with chlorine as it enters the
plant. Chemicals are added to form larger and heavier particles that settle
out. Fine particles are removed by filtration. A chlorine dose is added
to provide additional protection as the water leaves the plant and flows
into the distribution system.
The amount of chlorine and its contact time with
the water are controlled by government regulation. Enough chlorine has to
be added to disinfect the water inside the plant and to protect it from
disease causing organisms it encounters as it flows through the distribution
system. UV light or ozone may do a good job of disinfecting water in the
plant, but may not provide the residual needed to keep the water disinfected
until it is used. When UV light or ozone are used, a residual disinfectant
(typically chlorine or chloramine) is usually needed to ensure the quality
of the water.
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