Water contamination test, counting colonies of coliform-bacteria Escherichia coli (E. coli) per 100 milliliter of water. The counted result is expressed as ‘Coliform Microbial Density’ and indicates the extent of fecal matter present. According to common water quality standards, recreational (fishing and boating) water can have no more than 1000 colonies. Drinking water must be completely free from any colony, bathing and swimming pool water can have no more than 200 colonies.