Which method is commonly used to test for bacterial contamination in water?

The membrane filtration technique is a widely used method for testing bacterial contamination in water. This technique involves passing a water sample through a filter that captures bacteria present in the sample. After filtration, the filter is placed on a selective growth medium and incubated. This allows any viable bacteria to grow and form colonies, which can then be counted to estimate the bacterial concentration in the original water sample.

This method is particularly favored for its effectiveness in detecting both total coliforms and fecal coliforms, which are key indicators of microbial contamination and potential health risks associated with drinking water. It is suitable for a variety of water types, including drinking water, wastewater, and natural water sources.

In contrast, the other methods listed are not typically employed for bacterial testing in water. Gas chromatography is primarily used for analyzing gases and volatile compounds, colorimetric analysis is usually applied to measure concentrations of chemical substances based on color changes, and atomic absorption spectroscopy focuses on measuring concentrations of metal ions. None of these techniques specifically target bacteria, making the membrane filtration technique the most appropriate choice for this purpose.