What does CFU stand for in the context of water quality testing?

In the context of water quality testing, CFU stands for "Colony Forming Units." This term is crucial because it refers to the unit used to estimate the number of viable microorganisms in a sample. When testing water, particularly for the presence of bacteria, the sample is cultured on a growth medium. Each individual bacterium that reproduces and forms a visible colony on the medium is considered a colony forming unit. This measurement allows scientists and technicians to determine the concentration of bacteria in water, which is essential for assessing water safety and quality.

The other choices do not accurately describe this concept, as there are no recognized definitions for colony filtering units, contaminant forming units, or cultural formulating units in water quality testing. Thus, the distinction of "Colony Forming Units" is critical in microbiological assessments of water.