| Term | Definition |
| colony forming units (cfu) | The number of bacteria in a sample that can form colonies. |
| E. coli | Escherichia coli; Gram-negative bacteria often located in the colon (large intestines) of warm-blooded animals. The presence of E. coli in a water sample often indicates fecal contamination, and some strains of this bacteria can cause serious illnesses in humans. |
| heterotrophic bacteria | bacteria that use organic compounds (carbon-containing compounds) as food sources. |
| heterotrophic plate count (HPC) | a microbiological method used to determine the density of heterotrophic bacteria in a sample. Criterion Water Labs reports this as the number of colony-forming units (cfu) per 1 mL of water. In this method, a known amount of a water sample is incubated with a food source such as agar, and after a pre-determined amount of time, the number of distinct bacterial colonies are counted. The higher the bacterial density, the higher the heterotrophic plate count. |
| total coliforms | types of bacteria commonly found in the colon (large intestines) of warm-blooded animals. While not all coliforms cause diseases in humans, the presence of total coliforms in a water sample often indicates fecal contamination, and fecal material can be pathogenic. |
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