During coliform analysis using the presence-absence test, the sample should be incubated for how long?

The correct incubation period for coliform analysis using the presence-absence test is 24 to 36 hours at 25 degrees Celsius. This timeframe allows sufficient time for any coliform bacteria present in the water sample to multiply to detectable levels, while the temperature is conducive to microbial growth without being excessively warm, which could favor the growth of non-target organisms.

The presence-absence test is designed to provide a simple yes or no answer regarding the presence of coliform bacteria in a water sample. When incubated at the specified temperature and duration, the results obtained will be more reliable, as they follow standard methods in microbiological testing. This allows water operators to effectively determine the safety of the water based on the presence of potentially harmful bacteria.