The presence of microorganisms in drinking water is determined by:

Explanation

Biochemical oxygen demand (BOD) is a chemical procedure for determining the amount of dissolved oxygen needed by microorganisms in a body of water to break down organic material present in a given water sample at a certain temperature over a specific period. The greater the value of BOD, the more rapidly oxygen is depleted in water bodies. This means less oxygen is available to higher forms of aquatic life.