The Total Coliform Rule requires that drinking (culinary)
water be free from contamination with total coliforms.
Total coliforms are not necessarily dangerous themselves, but
are indicators of the possibility of water contamination. The
most common method of screening for total coliforms is via
media containing ONPG, which is cleaved by the enzyme galactosidase,
found in total coliforms. The ONPG cleavage product produces
a yellow color. The genera typically found in environmental
samples that are positive for total coliforms are Klebsiella,
Citrobacter, Enterobacter, Serratia, Hafnia, and other members
of the Enterobacteriaceae.
A subset of total coliforms is fecal coliforms. (In
other words, all fecal coliforms are also total coliforms,
but not all total coliforms are fecal coliforms.) Currently,
fecal coliforms are identified via the presence of beta-glucuronidase
hydrolyzing MUG to produce a product that is fluorescent under
UV light. In most cases, only Escherichia coli is identified,
and thus E. coli is the primary fecal coliform of concern.
However, a few other species of Escherichia, as well as a few
Shigellas and Salmonellas are beta-glucuronidase positive.
Unfortunately, the enterohemorrhagic E. coli, O157:H7
is MUG negative and would only appear as a total coliform,
not as a fecal coliform.
Fecal coliforms are considered to be better indicators of
fecal contamination than are total coliforms. Thus, water systems
that test as total coliform positive (but fecal coliform negative)
merely retest to identify the source of the contamination.
In many cases, the total coliforms are part of a biofilm on
the inside of the distribution pipes.
Development of a biofilm begins with the deposition of a conditioning
layer of organic matter on the surface to be colonized. This
layer acts as a buffer to neutralize excessive surface charge,
thus allowing cells to approach. Cells attach to the surface
then begin to form a glycocalyx (a voluminous, loosely organized,
carbon expansive mat formed by starving cells). The glycocalyx
acts as a charged net to entrain nutrients similar to an ion
exchange resin. Nutrient materials accumulate and the cells
reproduce. Accumulation of wastes rarely limits the size of
the biofilm, because secondary colonizers metabolize the wastes
from the primary colonizers. Biofilms are difficult to disinfect
because the polysaccharide network protects the organisms.
Monochloramines are more effective than free chlorine at reducing
biofilms.
If fecal coliforms are found in drinking water, then resampling
takes place immediately. Further isolation of fecal coliforms
will lead to public notification and boil water advisories.
The Utah Public Health Laboratory will identify all fecal coliforms
for water systems considering public notification or boil water
advisories.
Another important subset of indicator organisms is aerobic
spores. Dr. Eva Nieminski, of the Utah Department of
Environmental Quality, has spearheaded research to show that
these indicator organisms can be used as a means of assessing
the efficacy of water filtration systems.
Information on how to collect samples for each of these tests
can be found in the Microbiology Client Services Manual.
Individuals who obtain their drinking water from private wells
soon learn that the complex assortment of rules and regulations
specifically exempt private wells. Therefore, most people with
private wells do not routinely test their water for the presence
of microbial contamination. These tests are inexpensive and
can be obtained from a number of private laboratories statewide
(look in the yellow pages under Laboratories).
We strongly urge private well owners to check their water
for the presence of total coliforms (an indicator of possible
microbial contamination) at least annually. When total coliforms
are found, you should decontaminate your well head and recollect
another sample in two weeks. Contact your local health department
for instructions on collecting samples and decontaminating
well heads.
A recent study, sponsored by the National Center for Environmental
Health (a part of the Centers for Disease Control and Prevention
in Atlanta) noted that people whose wells are "older than
25 years, shallower than 100 feet, or greater than six inches
in diameter were more likely to have contaminants than samples
from households with a newer, deeper, and smaller-diameter
drilled or driven well."
Potential contamination sources can be found within 100 feet
of the well head and include septic tanks, fields, and structures
that contain fecal material.
This report is available on line at http://www.cdc.gov/nceh/programs
