Bacteria are unicellular organisms that rapidly multiply in a warm environment and especially in water, depending on nutrient supply. Under favourable conditions, bacteria divide under less than 10 minutes. Size of bacteria: E. coli, Salmonella, Cholera,from 0.2 to 5 microns
- Heterotrophic bacteria = Building essential substances critical for life from organic carbon;Example: food utilization in humans, animals
- Autotrophic bacteria = ability of living organisms and plants to build their materials from inorganic substances, Example: photosynthesis in plants
Total coliform bacteria
This deals with bacteria indicators. In contrast to the faecal coliform, these bacteria which are found both in the intestine as well as in the free nature may proliferate, if they find enough food substances. Like faecal coli, the total coliform bacteria are not actual infection pathogens. However, they settle well in open wounds. This then leads to suppuration. The main reason in search for these organisms is that their multiplication can be estimated and the presence of other potentially pathogenic intestinal bacteria in the water can be ascertained. 
The concentration of total coliform bacteria is usually measured in CFU/100 ml, CFU / ml in accordance with German Association for Rainwater Harvesting and Water Utilisation!
Faecal coliform bacteria = heat tolerant coliform and E. coli
These bacteria are normally found in the intestines of humans and mammals, but are usually harmless. These bacteria do not multiply outside the human body - especially in the bathing water. Therefore, they are a useful indicator of contamination by human waste. The presence of faecal coli may simultaneously comprise of other pathogens that may also be present in the intestine. Inversely, if there are no faecal coli in the bathing water, then you can be pretty sure that no other harmful intestinal bacteria are present in the water. 
The concentration of faecal coliform bacteria is usually measured in CFU/100 ml = E.Coli = similar coliform = heat tolerant.
Intestinal Enterococci (Synonym: Faecal streptococci)
A positive detection of enterococci indicates the high probability of faecal contamination. The bacteria hardly multiply in the water and are an evidence of past contamination. They are particularly resistant to chlorine.
It is a common soil and water bacteria and may be segregated from plants, fruits, food and the intestinal tract of humans and animals. It is considered an important nosocomial bacterial and food spoiler and may be found in mains water, washbasin, dishwasher, medicines and disinfectants.
- ISA – Institut für Siedlungswasserwirtschaft der RWTH Aachen