- Drinking Water Parasitology
- Surface Water Bacteriology
- Swimming Pools and Recreational Water Bacteriology
- Environmental Hazards, including Legionella and Mycobacterium avium intracellulare
- Testing Private Wells
Drinking Water Bacteriology
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.
Microbial Contamination of Private Wells
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.