The presence of dissolved oxygen (DO) in a water body is critical for water quality and the support of aquatic life. Demands on DO via biochemical and chemical degradation of organic and inorganic pollutants are of great importance to water quality management. With this background, the measurement of biochemical oxygen demand (BOD) was identified as a good standard indicator of water quality over 100 years ago,1 with lower BOD levels reflecting higher levels of water quality. We argue that the standard BOD-measurement method, ISO 5815-1, is routinely underestimating the DO demand in a water body by employing routine suppression of oxygen demand from the nitrification process of converting ammonium to nitrate. Underestimation of the actual oxygen demand may subsequently cause systemic risk in environmental impact assessments.