Which common indicator is used to measure organic pollution in water?

The measurement of organic pollution in water is effectively indicated by Biochemical Oxygen Demand (BOD). BOD assesses the amount of oxygen that bacteria will consume while decomposing organic matter in a water sample over a specified period, usually five days at a controlled temperature. When organic pollutants are present, they lead to increased oxygen consumption, thus resulting in higher BOD values. A high BOD indicates significant organic pollution, which can deplete dissolved oxygen levels in water, harming aquatic life.

In contrast, options like pH value indicate the acidity or alkalinity of the water but do not specifically measure organic pollution. Turbidity levels measure the cloudiness or clarity of water, affected by suspended particles, but do not directly relate to organic content. Lastly, while coliform bacteria counts assess the presence of potentially harmful microorganisms and indicate fecal contamination, they do not directly measure organic pollution. Therefore, BOD is the most relevant indicator of organic pollution among the provided choices.