Meaning of Biological Oxygen Demand (BOD): In water quality and wastewater engineering, the term BOD is primarily used in relation to which type of water?

Introduction / Context:
Biological Oxygen Demand (BOD) quantifies the biodegradable organic load in a water sample by measuring the oxygen consumed by microorganisms over a standard period. It is a cornerstone metric for wastewater characterisation and treatment design.

Given Data / Assumptions:

• BOD is measured in mg/L, typically over 5 days at 20°C.
• The question contrasts clean water uses with wastewaters.

Concept / Approach:
BOD is most relevant for waste streams—municipal sewage and industrial effluents—where biodegradables are present. While potable, cooling, and distilled waters should have extremely low BOD, engineers apply BOD to evaluate and regulate discharges from industries and sewage works. Thus, among the choices, industrial effluents best matches the context in which BOD is routinely referenced, specified, and limited by permits.

Step-by-Step Solution:

Verification / Alternative check:
Discharge consents typically stipulate BOD limits; drinking water standards do not rely on BOD as a core parameter.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing BOD with COD; COD is a complementary, faster chemical test but measures all oxidisable matter, not just biodegradable.

Final Answer:
industrial effluents