Nitrite limit in potable water:\r What is the permissible amount of nitrites (NO2–) present in safe drinking water supplied to consumers?

Introduction / Context:
Nitrite (NO2–) is an intermediate in the nitrogen cycle and a potential indicator of incomplete nitrification or contamination. Elevated nitrite poses health risks, especially methemoglobinemia in infants. Water supply standards therefore set very stringent limits for nitrite in finished water.

Given Data / Assumptions:

• Finished water after treatment is being considered.
• Public health protection is the priority.
• Conservative exam-oriented guidance often treats nitrite as undesirable and to be absent.

Concept / Approach:
While specific numerical limits vary by jurisdiction, many education syllabi emphasize that nitrite should be absent in distributed water. Hence, the safest and commonly accepted response in basic water quality questions is “Nil”. This reflects the operational target rather than a nuanced regulatory table that may list very small allowable concentrations.

Step-by-Step Solution:
Recognize nitrite as a contaminant indicating biological instability or pollution.Recall that potable supply management aims for nondetectable nitrite.Select “Nil” as the permissible amount for exam purposes.

Verification / Alternative check:
Utilities closely monitor nitrification in chloraminated systems to keep nitrite undetectable; early detection triggers corrective actions (e.g., boosting disinfectant, flushing, converting to free chlorine temporarily).

Why Other Options Are Wrong:

• 10–45 ppm values are far above health-based guideline levels and would be unacceptable in drinking water.

Common Pitfalls:

• Confusing nitrate (NO3–) limits with nitrite limits; nitrate limits are much higher than nitrite.
• Assuming a small allowable concentration is acceptable in practice; operations typically target non-detect for safety.

Final Answer:
Nil