For treated potable water, what should be the biochemical oxygen demand (BOD) level?

Introduction / Context:
BOD measures the oxygen consumed by microbial oxidation of biodegradable organics. In drinking-water treatment, the objective is to remove biodegradable organic matter to prevent regrowth and ensure biological stability in distribution systems.

Given Data / Assumptions:

• Treated water destined for human consumption.
• Standard treatment includes coagulation–filtration and disinfection.

Concept / Approach:
While laboratory detection limits exist, design/operations aim for effectively zero biodegradable organics (BOD ≈ nil) in finished water. Regulatory frameworks typically focus on surrogate parameters (TOC, assimilable organic carbon) and microbial indicators, but the teaching convention is that potable water should have no measurable BOD.

Step-by-Step Solution:

Verification / Alternative check:
Operational practice in potable systems aims for biologically stable water; measurable BOD values like 10–30 mg/L are characteristic of wastewater, not drinking water.

Why Other Options Are Wrong:

• 10–30 ppm (mg/L) are far too high and typical of wastewater, not finished drinking water quality.

Common Pitfalls:

• Confusing wastewater effluent standards (BOD) with drinking water goals (very low organics, stable water).

Final Answer:
Nil