Identify the incorrect statement regarding BOD (Biological Oxygen Demand) as a water quality parameter.

Introduction / Context:
Biological Oxygen Demand (BOD) indicates the amount of dissolved oxygen that aerobic microorganisms require to oxidize biodegradable organic matter in water over a specified period (commonly 5 days at 20°C, termed BOD5). It is a key indicator of organic pollution and treatment performance.

Given Data / Assumptions:

• Options include statements about the definition, units, and typical magnitude of BOD.
• Potable (drinking) water is expected to have very low BOD.

Concept / Approach:
Evaluate each statement against standard definitions and typical values. The incorrect one will contradict accepted ranges for drinking water quality.

Step-by-Step Solution:

Verification / Alternative check:
Regulatory guidance and design manuals consistently place potable water BOD very low; secondary effluent may be around 20 mg/L, raw sewage 150–300 mg/L, underscoring the scale difference.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing BOD with COD; thinking BOD is a substance that can be filtered out; assuming drinking water may have multi-mg/L BOD.

Final Answer:
Typical BOD for potable water is about 2.5 mg/L.