Which of the following types of bacteria are often found in drinking water?

The correct answer is Escherichia coli, often abbreviated as E. coli, which is a type of bacteria commonly found in drinking water. E. coli serves as an important indicator of water quality and safety because its presence indicates possible fecal contamination, which can carry pathogens that cause waterborne diseases.

While Cryptosporidium is a pathogen often associated with waterborne outbreaks, it is actually a protozoan parasite and not a bacteria. It can contaminate drinking water, but it does not fit in the same categorization as the other bacterial options listed.

Staphylococcus, while a diverse group of bacteria, is more commonly found on the skin and in the respiratory tract and does not typically indicate drinking water contamination.

Streptococcus, similar to Staphylococcus, comprises various bacterial species and is usually associated with other infections rather than indicating drinking water safety.

Therefore, E. coli is used as a reliable measure to assess the microbiological safety of drinking water due to its significance in indicating fecal contamination and potential health risks associated with polluted water.