Minimum level of free chlorine in potable water is: (Repeat)
**Core Concept**
The minimum level of free chlorine in potable water is a critical parameter for ensuring water safety and preventing waterborne diseases. **Free chlorine** refers to the amount of chlorine available to inactivate bacteria, viruses, and other pathogens. The World Health Organization (WHO) and other health agencies have established guidelines for the minimum acceptable levels of free chlorine in drinking water.
**Why the Correct Answer is Right**
The correct answer is based on the recommendation that the minimum level of free chlorine in potable water should be at least 0.5 mg/L after at least 30 minutes of contact time. This concentration is considered sufficient to inactivate most pathogens, including bacteria, viruses, and protozoa. The **disinfection process** involves the reaction of free chlorine with organic matter and microorganisms, leading to their inactivation or death.
**Why Each Wrong Option is Incorrect**
**Option A:** Is incorrect because it is lower than the recommended minimum.
**Option B:** Is incorrect because it is lower than the recommended minimum.
**Option D:** Is incorrect because it exceeds the maximum allowable level of free chlorine, which can cause taste, odor, and health problems.
**Clinical Pearl / High-Yield Fact**
Remember, the minimum level of free chlorine is crucial for preventing waterborne diseases, such as cholera and typhoid fever. Always check the free chlorine level in potable water, especially in emergency or low-resource settings.
**Correct Answer:** C. 0.5 mg/L