Drinking Water Advisory Communication Toolbox
Section 1. Tools & Templates: Before an Event: Frequently Asked Questions About Coliforms and Drinking Water
Frequently Asked Questions About Coliforms and Drinking Water
What are coliforms?
Coliforms are a group of bacteria found in plant material, water, and soil. Coliforms are also present in the
digestive tracts and feces of humans and animals. Most of the time, these bacteria are not harmful.
Why does a water system test for coliforms?
Water systems test for indicators such as total coliforms, fecal coliforms, or E. coli to monitor water
quality. If the water system has a positive test for one of these indicators, it can mean recent
contamination with soil or human feces.
What does a positive coliform test result mean?
A positive coliform test means possible contamination and a risk of waterborne disease. A positive
test for total coliforms always requires more tests for fecal coliforms or E. coli. A confirmed positive
test for fecal coliforms or E. coli means you need to take action as advised by your water system.
Will coliform bacteria make me sick?
Most coliform bacteria are a normal part of the environment. They do not cause disease but do
indicate the water might be contaminated by soil or feces. Some rare types of coliforms, such as E.
coli O157:H7, can cause serious illness. Although most E. coli O157:H7 outbreaks are from eating
raw or undercooked food, cases from contaminated drinking water can occur, but are rare.
Why test for indicator organisms?
A biological pathogen is any organism, such as a bacteria, virus, protozoa, or parasite, that causes a
disease. Biological pathogens are commonly called “germs.” There are many different possible
pathogens. It is not possible to test for every type of pathogen in every water sample, so water systems
use indicators instead.
Water systems test for indicator organisms, like coliforms, to check for possible contamination by
biological pathogens. Most coliforms are not harmful, but they come from the same sources as other
bacteria and organisms that could make you sick.
Section 1. Tools & Templates: Before an Event: Frequently Asked Questions About Coliforms and Drinking Water 1
Developed by the Centers for Disease Control and Prevention and the American Water Works Association in collaboration with the U.S. Environmental Protection Agency and ot her partners.
March 2013 - http://www.cdc.gov/healthywater/emergency/dwa-comm-toolbox/tools-templates-main.html
Drinking Water Advisory Communication Toolbox
Section 1. Tools & Templates: Before an Event: Frequently Asked Questions About Coliforms and Drinking Water
Frequently Asked Questions About Coliforms and Drinking
Water, cont’d
What are “indicator” organisms?
Indicator organisms come from the same sources as organisms that make you sick. Indicator
organisms are easier to identify, are present in larger numbers, and respond to water treatment the
same way as harmful bacteria and many other biological pathogens. A biological pathogen is any
organism, such as a bacteria, virus, protozoa, or parasite, that causes a disease. Biological pathogens
are commonly called “germs”.
• Total coliforms is another term for the full group of coliforms. They are indicators of possible
water contamination.
• Fecal coliforms are one type of coliform bacteria that is found found mainly in animal digestive
tracts and feces. Fecal coliforms are a more specific indicator of fecal contamination of water.
• E. coli (Escherichia coli) is a species of fecal coliform bacteria. E. coli almost always comes
from animal feces. E. coli is considered the best indicator of fecal water contamination. If E. coli
is present, harmful bacteria or other pathogens may also be present.
For more information see or contact:
• Personal Preparation and Storage of Safe Water: CDC provides guidance on the amount of
water needed for good health, as well as how to prepare and store safe water before and during
an emergency.
• Hygiene and Handwashing: CDC provides guidance on alternative hygienic practices when
water is not available or is contaminated.
• A Guide to Water Filters: CDC maintains a guide for filters that remove Cryptosporidium or
Giardia.
• EPA Safe Drinking Water Hotline: 1-800-426-4791
• Consumer Information: EPA provides information and guidance about drinking water quality,
emergencies, contaminants, public health issues, and treatment and storage.
• Water system: [name, title, phone, e-mail, website]
• State or local public health department: [name, title, phone, e-mail, website]
• Primacy Agency: [name, title, phone, e-mail, website]
Section 1. Tools & Templates: Before an Event: Frequently Asked Questions About Coliforms and Drinking Water 2
Developed by the Centers for Disease Control and Prevention and the American Water Works Association in collaboration with the U.S. Environmental Protection Agency and ot her partners.
March 2013 - http://www.cdc.gov/healthywater/emergency/dwa-comm-toolbox/tools-templates-main.html
