**Core Concept**
The World Health Organization (WHO) has established guidelines for drinking water quality to ensure public health. These guidelines include parameters such as color, pH, chloride, turbidity, and zinc, among others. The recommended values for these parameters are crucial for assessing the safety of drinking water.

**Why the Correct Answer is Right**
The correct answer choice is **d) Turbidity <5 NTU**. Turbidity measures the cloudiness or haziness of water caused by suspended particles. WHO recommends that the turbidity of drinking water should be less than 5 nephelometric turbidity units (NTU) to prevent the growth of bacteria and other microorganisms. This is because high turbidity can reduce the effectiveness of disinfection processes and allow pathogens to survive. **Why Each Wrong Option is Incorrect** **Option a:** Colour < 15 TCU (true) - While color is an important parameter, it is not the correct answer choice in this question. **Option b:** pH 6.5–8.5 (true) - WHO recommends a pH range of 6.5-8.5 for drinking water, but this is not the correct answer choice. **Option c:** Chloride 200–600 mg/1 (false) - WHO recommends a chloride level of less than 250 mg/L in drinking water, not 200-600 mg/L. **Option e:** Zinc < 4 mg/1 (true) - WHO recommends a zinc level of less than 3 mg/L in drinking water, but this is not the correct answer choice. **Clinical Pearl / High-Yield Fact** It's essential to note that the WHO guidelines for drinking water quality are regularly updated to reflect new scientific evidence and emerging health concerns. Healthcare professionals should stay informed about the latest guidelines to ensure the provision of safe drinking water to the public. **Correct Answer: D. Turbidity <5 NTU**