WHAT ARE THEY
Coliforms are a broad class of bacteria found in the environment.
It's chocolate ice cream, but you get the point
WHERE DO THEY COME FROM
Both the harmful and non-harmful bacteria primarily come from the feces of humans and other warm-blooded animals. They can also come from rotting vegetation. The presence of non-harmful coliform bacteria in drinking water may indicate a possible presence of harmful, disease-causing organisms.
HARMFUL VS. NON-HARMFUL
Most Coliform bacteria do not cause disease. Coliforms are broken into 3 groups:
Total Coliforms They include bacteria that are found in the soil, in water that has been in influenced by surface water, and in human or animal waste.
Fecal Coliforms both harmful and non-harmful: They are the group of the total coliforms that are considered to be present specifically in the gut and feces of warm-blooded animals
- Coli - a subgroup of the Fecal Coliforms: Some strains of E. Coli can cause serious illness.
PROLIFIC VS. NON-PROLIFIC
E.Coli is generally not found growing and reproducing in the environment. Total Coliforms (of the non-harmful type) are very prolific and once introduced to a surface can spread quickly. These non-harmful types include both fecal and non-fecal Coliforms.
COLIFORMS AND CLEANLINESS
The spread of Coliforms can be combated through good Hygiene. Simple washing with soap and water will prevent the spread of them.
SPREAD OF COLIFORMS
Coliforms can spread by touching the clean end of the filter with a dirty hand, by animal contact, or even by dust particles. Proper hygiene techniques must be taught with the use of the filters. Otherwise, contamination of the discharge side occurs. This is supported both by the Tuft’s study and the Messiah/John Hopkins study referenced later in this handout. 
TESTING FOR COLIFORMS
Because Total Coliforms reproduce very quickly they are easy to test for. A high indication of total Coliforms is usually a good and inexpensive way to determine if water needs treatment but it does not guarantee the presence of E. Coli. This type of testing is broad and encompasses most of the non-harmful types of Coliforms.
COMMON MISTAKES MADE WITH TESTING
Because the Total Coliform testing is inexpensive most people believe it is a simple way to see if the filter is working. What they really end up testing is not that the filter is working, but whether or not the discharge end has been contaminated. It only takes a few Coliform bacteria on the discharge to contaminate the sample. Once contaminated the bacteria very quickly grow in the test solution giving a positive test result. 
HOW TO PROPERLY TEST A FILTER
There is no quick and easy field test to see if a filter is working. Even an E. Coli test can yield false positive results if the discharge end of
the filter is not clean. Simply running water through the filter and doing a total Coliform test does not prove if the filter is working or not. Unless the filters discharged has been cleaned of ALL bacteria, you are going to get a false positive result. People believe that because they processed their sample correctly, they tested the filter correctly. They do not take into account the contamination that could have occurred on the discharge side of the filter and wrongly assume the filter is not functioning. Every time we hear of filter failure it always turns out to be procedural errors. Backwashing and pushing will remove the harmful bacteria, but will not remove all the bacteria. A few non-harmful bacteria that remain will multiply very quickly and yield a false positive test result.