This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
Permissible level of fluoride in drinking water as per WHO is: 
Select and explain. 
A. 0.5 mg/litre, B. 1.0 mg/litre, C. 1.5 mg/litre, D. 2.5 mg/litre
C: 1.5 mg/litre
Answer: C: 1.5 mg/litre 
Explanation: As per WHO, permissible limit of fluoride in drinking water is 1.5 mg/ litre. As per Bureau of Indian Standards (BIS), it is 1 mg/ litre. Dental fluorosis has been repoed with exposure to levels > 1.5 mg/ litre. Skeletal fluorosis has been repoed on exposure between 3 to 6 mg/ litre. Ref: Park, 21st Edition, Page 668