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The
Minnesota Department of Health
Background/Overview
Biological organisms
are among the oldest health threats to drinking water quality and the agents
currently responsible for most waterborne diseases.
They are the most
common contamination incident water operators will encounter.
Organisms known
to cause disease include bacteria, protozoa, and viruses; some algae and
helminths (worms) may also be capable of producing disease.
These
disease-causing organisms thrive in the intestines of warm-blooded animals.
They are easily transmitted to drinking water if the feces of an animal
contaminates a water supply for which there is not suitable disinfection.
Potential sources
of contamination include sewers, septic systems, feedlots, and animal yards.
Role of coliforms in
detecting contamination
Unfortunately,
specific disease-producing (pathogenic) organisms present in water are not
easily identified. It would be very difficult, expensive, and time consuming to
monitor for them.
For this reason,
it is necessary to select an easily measured “indicator organism,” whose
presence indicates that pathogenic organisms may be present.
A group of
closely related bacteria, the total coliform, has been selected as an indicator
of harmful organisms in drinking water.
Sources of coliform
bacteria
Total coliform
(TC) bacteria are common in the environment (such as in soil) and the
intestines of animals and are generally not harmful.
Escherichia coli (E.
coli) bacteria are found in greater quantities than total coliform in
animal fecal matter.
If E.
coli is detected along with TC in drinking water, there is strong
evidence that sewage is present; therefore, a greater potential for pathogenic
organisms exists.
Response to coliform
detection
MDH monitors
drinking water for public water supplies (PWSs) on a routine basis. If E.
coli is detected in the distribution system of a PWS, the system must
be disinfected.
In most cases
this includes emergency chlorination, which can last for two to five days. At
the same time a system is being disinfected, customers of the PWS are ordered
to vigorously boil their drinking and cooking water (Boil Water Advisory) for
one minute before using it.
Once the system
has been disinfected and flushed, the MDH tests the water again for coliform
bacteria. If none are detected, the Boil Water Advisory is lifted.
If only TC is detected
(without the presence of E. coli), the source is most likely
from contamination from the environment, introduced during construction or
while repairs to plumbing or a water main were underway.
The system will
identify the source of the contamination, correct the problem, and thoroughly
disinfect its system.
The public will
also be notified of the situation; however, unless unusual circumstances exist
to cause particular concern about the safety of the water, a Boil Water
Advisory will not be issued.
Exceptions
Total coliforms
are not a perfect indicator of the actual or potential presence of harmful
organisms.
Some
disease-producing organisms, especially protozoa such as Giardia and Cryptosporidium, are
able to withstand treatment which kill the total coliform.
These two
protozoa are often found in surface waters (the principle carriers of these
organisms) contaminated by human sewage or wildlife.
However, for the
majority of PWSs this is not a significant threat since most PWSs obtain their
water from wells rather than surface-water sources such as rivers and lakes.
For those PWSs
that use surface water, a combination of coagulation, filtration, and
disinfection has been successful and is recommended to reduce the risk of Giardia or Cryptosporidium contamination.
Health effects
Symptoms of
waterborne diseases may include gastrointestinal illnesses such as severe
diarrhea, nausea, and possibly jaundice as well as associated headaches and
fatigue.
It is important
to note, however, that these symptoms are not associated only with
disease-causing organisms in drinking water.
They may also be
caused by a number of other factors. In addition, not all people will be
affected to the same degree; young children and the elderly are usually more
susceptible.
The
Minnesota Department of Health (MDH) is the state authority for drinking
water. Several programs at MDH work together to ensure safe and adequate
drinking water. The Drinking Water Protection program focuses on public water
supplies. Public water supplies serve 25 people or more in places where they
live, work, gather and play.
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