The presence of bacteria and pathogenic (disease-causing) organisms is a concern when considering the safety of drinking water. Pathogenic organisms can cause intestinal infections, dysentery, hepatitis, typhoid fever, cholera, and other illnesses.
Sources of Bacteria in Drinking Water
Human and animal wastes are a primary source of bacteria in water. These sources of bacterial contamination include runoff from feedlots, pastures, dog runs, and other land areas where animal wastes are deposited. Additional sources include seepage or discharge from septic tanks, sewage treatment facilities, and natural soil/plant bacteria. Bacteria from these sources can enter wells that are either open at the land surface, or do not have water-tight casings or caps.
Insects, rodents or animals entering the well are other sources of contamination. Old wells were dug by hand and lined (cased) with rocks or bricks. These wells usually have large openings and casings that often are not well-sealed. This makes it easy for insects, rodents, or animals to enter the well.
Another way bacteria can enter a water supply is through inundation or infiltration by flood waters or by surface runoff. Flood waters commonly contain high levels of bacteria. Small depressions filled with flood water provide an excellent breeding ground for bacteria. Whenever a well is inundated by flood waters or surface runoff, bacterial contamination is likely. Shallow wells and wells that do not have water-tight casings can be contaminated by bacteria infiltrating with the water through the soil near the well, especially in coarse-textured soils.
Older water systems, especially, dug wells, spring-fed systems and cistern-type systems are most vulnerable to bacterial contamination. Any system with casings or caps that are not water-tight are vulnerable. This is particularly true if the well is located so surface runoff might be able to enter the well. During the last five to 10 years, well and water distribution system construction has improved to the point where bacterial contamination is rare in newer wells.
Indications of Bacteria
Bacterial contamination cannot be detected by sight, smell or taste. The only way to know if the water suppy contains bacteria is to have it tested.Potential Health Effects
Coliform bacteria may not cause disease, but can be indicators of pathogenic organisms that cause diseases. The latter could cause intestinal infections, dysentery, hepatitis, typhoid fever, cholera and other illnesses. However, these illnesses are not limited to disease-causing organisms in drinking water. Other factors not associated with drinking water may be the cause.
Intestinal infections and dysentery are generally considered minor health problems. They can, however, prove fatal to infants, the elderly, and those who are ill. Today typhoid, hepatitis and cholera are rarely encountered in the United States. Other bacteria also may be present in water. No specific sanitary significance or health standards have been indicated for non-pathogenic non-coliform bacteria.
Drinking Water TestingColiform bacteria originate in the intestinal tract of warm-blooded animals and can be found in their wastes. Coliform bacteria 
can also be found in soil and on vegetation. Coliform bacteria are relatively simple to identify and are present in much larger numbers than more dangerous pathogens. Coliform bacteria react to the natural environment and treatment processes in a manner and degree similar to pathogens. By monitoring coliform bacteria, the increase or decrease of many pathogenic bacteria can be estimated.Due to this association, bacterial safety of drinking water is monitored by testing for coliform bacteria Interpreting Test Results
The EPA establishes standards for drinking water which fall into two categories -- Primary Standards are based on health considerations, and are designed to protect people from three classes of toxic pollutants: pathogens, radioactive elements and toxic chemicals.
Bacterial contamination falls under the category of pathogens. The EPA Maximum Contaminant Level (MCL) for coliform bacteria in drinking water is zero (or no) total coliform per 100 ml of water. The number of coliform colonies found in the incubated water sample, if any, is reported and the form is checked to indicate whether or not the water meets the EPA bacteriological standard of zero. At times, excessive numbers of other bacteria in a sample can interfere with the counting of coliform types. These samples may be classified as "too numerous to count" or "confluent growth."
If the laboratory report indicates the presence of coliforms, or states "too numerous to count," or "confluent growth," the Department of Health recommends another sample be analyzed to help evaluate the contamination. If you suspect bacterial contamination in your water supply, use an alternative water supply or disinfect your water supply while waiting for test results.
Total Coliform Bacteria Testing
COLIFORM BACTERIA
The total coliform bacteria test is a primary indicator of "potability" , suitability for consumption, of drinking water. It measures the concentration of total coliform bacteria associated with the possible presence of disease causing organisms.
