While many types of coliform bacteria present in well water are harmless, dangerous coliform bacteria cause fever, diarrhea, abdominal cramps and other forms of gastrointestinal upset, according to Penn State College of Agricultural Sciences. Some rare types of coliform bacteria can cause severe illness or death. Typically, children and the elderly are more likely than healthy adults to be affected by these types of bacteria in well water.
Even though most types of coliform bacteria are harmless, a healthy source of ground water does not normally host these microorganisms, notes the Water Quality and Health Council. The presence of coliform bacteria indicates a microbial contamination. Common contamination causes include flooding, overall quality of water within the region, and the presence of a septic tank near the well. Homeowners can disinfect the well themselves using sodium hypochlorite or calcium hypochlorite once someone addresses the cause of the contamination.
Coliform bacteria is a term for many different types of bacteria found in plant material, soil material, and animal and human waste, explains the New York State Department of Health. Dangerous pathogens that cause serious disease can be difficult to detect in well water, so a total coliform bacteria test acts as an indicator of the possibility that pathogenic bacteria are present. A fecal coliform test better assesses the chance of pathogenic bacteria, while an Escherichia coli test is the best option for determining the possible presence of harmful pathogens.