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E. coli and coliform bacteria in well water Risk assessment report
Download the full report above under files and media.
Executive summary
Pathogenic microorganisms can spread through drinking water and cause both acute and chronic disease. Pathogenic micro-organisms spread through drinking water include a
wide range of viruses, bacteria and parasitic protozoa (single-celled organisms).
Since disease-causing microorganisms found in drinking water mainly originate from fecal contamination (contamination from feces), the microbiological quality of drinking water is assessed by measuring the presence of the indicator bacterium E. coli.
Findings of this bacterium provide a measure of the degree of fecal contamination and thus, indirectly, of the risk of disease.
Other parameters measured are coliform bacteria and total bacteria count. As several species in these groups can degrade plant material and thus multiply in nature, they are not as strongly
associated with fecal contamination as E. coli. However, they do provide a measure of well function and whether the water may be affected by surface water.
For individual water, the current guideline value for E. coli is 1/100 ml for water that is fit for human consumption and 10/100 ml for water that is not fit for human consumption. The corresponding guideline for coliform bacteria is 50/100 ml
for good with remark and 500/100 ml for unfit.
Epidemiological studies show an increased risk of gastroenteritis in children who drink water where E. coli bacteria have been found, but this association is not seen among adults. It is not these bacteria per se that
cause illness, but in most cases various intestinal viruses that mainly circulate between children under ten years of age before a stronger immunity is built up. Other factors contributing to a higher susceptibility in children
are that they have lower pepsin secretion in the stomach than adults and the mucosa of the gut is more permeable to water. There is also evidence that adults who drink water for the first time
from a contaminated water source are also at an increased risk of stomach illness.
A quantitative microbiological risk assessment was carried out to estimate what a safe level of water is.
It showed that the probability of gastroenteritis is greatly increased if the contamination comes from wastewater. If the contamination comes from manure, there is a slightly increased risk of enterohemorrhagic E. coli (EHEC). This means that no E. coli bacteria should be found in 100 ml samples for the quality to be comparable to municipal drinking water.
Coliform bacteria are not as associated with fecal contamination as E. coli. If an analysis of the water shows more than 50 coliforms per 100 ml sample, but no E. coli, consumption of the water is
unlikely to increase the risk of gastroenteritis. However, it is an indication that the well is not sealed and that there is a risk of contaminated surface water entering at other times.
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Download the full report above under files and media.
Executive summary
Pathogenic microorganisms can spread through drinking water and cause both acute and chronic disease. Pathogenic micro-organisms spread through drinking water include a
wide range of viruses, bacteria and parasitic protozoa (single-celled organisms).
Since disease-causing microorganisms found in drinking water mainly originate from fecal contamination (contamination from feces), the microbiological quality of drinking water is assessed by measuring the presence of the indicator bacterium E. coli.
Findings of this bacterium provide a measure of the degree of fecal contamination and thus, indirectly, of the risk of disease.
Other parameters measured are coliform bacteria and total bacteria count. As several species in these groups can degrade plant material and thus multiply in nature, they are not as strongly
associated with fecal contamination as E. coli. However, they do provide a measure of well function and whether the water may be affected by surface water.
For individual water, the current guideline value for E. coli is 1/100 ml for water that is fit for human consumption and 10/100 ml for water that is not fit for human consumption. The corresponding guideline for coliform bacteria is 50/100 ml
for good with remark and 500/100 ml for unfit.
Epidemiological studies show an increased risk of gastroenteritis in children who drink water where E. coli bacteria have been found, but this association is not seen among adults. It is not these bacteria per se that
cause illness, but in most cases various intestinal viruses that mainly circulate between children under ten years of age before a stronger immunity is built up. Other factors contributing to a higher susceptibility in children
are that they have lower pepsin secretion in the stomach than adults and the mucosa of the gut is more permeable to water. There is also evidence that adults who drink water for the first time
from a contaminated water source are also at an increased risk of stomach illness.
A quantitative microbiological risk assessment was carried out to estimate what a safe level of water is.
It showed that the probability of gastroenteritis is greatly increased if the contamination comes from wastewater. If the contamination comes from manure, there is a slightly increased risk of enterohemorrhagic E. coli (EHEC). This means that no E. coli bacteria should be found in 100 ml samples for the quality to be comparable to municipal drinking water.
Coliform bacteria are not as associated with fecal contamination as E. coli. If an analysis of the water shows more than 50 coliforms per 100 ml sample, but no E. coli, consumption of the water is
unlikely to increase the risk of gastroenteritis. However, it is an indication that the well is not sealed and that there is a risk of contaminated surface water entering at other times.
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Download the full report above under files and media.
Executive summary
Pathogenic microorganisms can spread through drinking water and cause both acute and chronic disease. Pathogenic micro-organisms spread through drinking water include a
wide range of viruses, bacteria and parasitic protozoa (single-celled organisms).
Since disease-causing microorganisms found in drinking water mainly originate from fecal contamination (contamination from feces), the microbiological quality of drinking water is assessed by measuring the presence of the indicator bacterium E. coli.
Findings of this bacterium provide a measure of the degree of fecal contamination and thus, indirectly, of the risk of disease.
Other parameters measured are coliform bacteria and total bacteria count. As several species in these groups can degrade plant material and thus multiply in nature, they are not as strongly
associated with fecal contamination as E. coli. However, they do provide a measure of well function and whether the water may be affected by surface water.
For individual water, the current guideline value for E. coli is 1/100 ml for water that is fit for human consumption and 10/100 ml for water that is not fit for human consumption. The corresponding guideline for coliform bacteria is 50/100 ml
for good with remark and 500/100 ml for unfit.
Epidemiological studies show an increased risk of gastroenteritis in children who drink water where E. coli bacteria have been found, but this association is not seen among adults. It is not these bacteria per se that
cause illness, but in most cases various intestinal viruses that mainly circulate between children under ten years of age before a stronger immunity is built up. Other factors contributing to a higher susceptibility in children
are that they have lower pepsin secretion in the stomach than adults and the mucosa of the gut is more permeable to water. There is also evidence that adults who drink water for the first time
from a contaminated water source are also at an increased risk of stomach illness.
A quantitative microbiological risk assessment was carried out to estimate what a safe level of water is.
It showed that the probability of gastroenteritis is greatly increased if the contamination comes from wastewater. If the contamination comes from manure, there is a slightly increased risk of enterohemorrhagic E. coli (EHEC). This means that no E. coli bacteria should be found in 100 ml samples for the quality to be comparable to municipal drinking water.
Coliform bacteria are not as associated with fecal contamination as E. coli. If an analysis of the water shows more than 50 coliforms per 100 ml sample, but no E. coli, consumption of the water is
unlikely to increase the risk of gastroenteritis. However, it is an indication that the well is not sealed and that there is a risk of contaminated surface water entering at other times.
Article number:
No files available.