Which of the following methods is primarily used in a presence/absence coliform test?

The presence/absence coliform test is primarily designed to determine whether coliform bacteria are present in a water sample. Colorimetric analysis is a method that involves detecting a color change in a sample when coliforms are present, indicating contamination. This method relies on specific reagents that react with coliform bacteria, resulting in a measurable color change that signifies the presence of these microorganisms.

In this context, colorimetric analysis is efficient because it allows for a straightforward visual determination of contamination without needing extensive laboratory equipment. This simplicity makes it particularly useful for quick assessments of water quality in compliance with regulatory requirements.

Temperature monitoring, while important in the context of microbiological testing, is not a method specifically used for the presence/absence of coliform bacteria. Conductivity measurement is more commonly associated with determining water salinity and ionic content, rather than specifically identifying coliform presence. The filtration method is another technique used for microbial analysis but involves more complex protocols and is not primarily designated for a simple presence/absence test.

Thus, colorimetric analysis is the appropriate method for indicating coliform contamination in the presence/absence test.