Bacteria refers to a wide range of microorganisms which include coliform, cyanbacteria (algae), staphylococcus, legionella pneumophila (Legionaires' disease), shigella dysenteriae (Dysentery), and escherichia coli (E. coli). Bacteria are some of the first forms of life to develop and can be found in almost every habitation the planet.
Testing for specific types of bacteria is time-consuming and costly. Instead, organizations like the EPA and local water providers will test for Coliform bacteria, as it is an indicator that a water supply could be contaminated.
There are multiple ways to disinfect drinking water. These are ultraviolet disinfection, continuous chlorination, shock chlorination, and distillation. Ultraviolet (UV) disinfection uses natural radioactive light to damage the DNA in microbes, preventing them from reproducing. Continuous chlorination disinfects using chlorine, however it will add a taste and odor to the water, not to mention trihalomethanes (THMs) can form when the chlorine interacts with organic matter present in the water. Shock chlorination uses chlorine as well, however this is a temporary solution. Distillation is the method of boiling water until it turns into steam, then re-condensing the steam back into water which kills any organism in the process. However distillation requires a lot of energy and time when compared with other purification methods.
NSF/ANSI Standard 55: Ultraviolet Microbiological Water Treatment Systems
Overview: This standard establishes requirements for point-of-use (POU) and point-of-entry (POE) ultraviolet systems and includes two optional classifications. Class A systems (40,000 uwsec/cm2) are designed to disinfect and/or remove microorganisms from contaminated water, including bacteria and viruses, to a safe level. Class B systems (16,000 uw-sec/cm2) are designed for supplemental bactericidal treatment of public drinking water or other drinking water, which has been deemed acceptable by a local health agency.
The foregoing information was compiled from the the links listed above.