Amount of free residual chlorine in drinking water: September 2007, March 2010
**Core Concept**
The amount of free residual chlorine in drinking water is a critical parameter for ensuring the water's safety from microbial contamination. Free residual chlorine is a measure of the amount of chlorine that remains in the water after the initial disinfection process, and it's essential for maintaining its antimicrobial properties.
**Why the Correct Answer is Right**
Free residual chlorine is typically measured in parts per million (ppm) and should be within the range of 0.2-1.0 ppm to effectively inactivate bacteria, viruses, and other microorganisms. This concentration range allows for adequate disinfection while minimizing the potential health risks associated with excessive chlorine levels. The World Health Organization (WHO) recommends a minimum free residual chlorine level of 0.5 ppm in drinking water to ensure its safety.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a free residual chlorine level of 0 ppm would render the water ineffective against microbial contaminants, increasing the risk of waterborne diseases.
**Option B:** This option is incorrect because a free residual chlorine level above 1.0 ppm could lead to unpleasant taste, odor, and potential health issues, such as gastrointestinal irritation and respiratory problems.
**Option C:** This option is incorrect because a free residual chlorine level below 0.2 ppm might not provide sufficient antimicrobial protection, allowing microorganisms to multiply and cause waterborne diseases.
**Clinical Pearl / High-Yield Fact**
The ideal free residual chlorine level in drinking water is a delicate balance between ensuring microbial safety and minimizing potential health risks. It's essential to regularly monitor and adjust the chlorine level to maintain an optimal concentration.
**Correct Answer: C. 0.2-0.5 ppm.**