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
What is the ideal hardness of drinking water in mEg/Litre? 
Select and explain. 
A. >3, B. <1, C. 3-Jan, D. >6
C: 3-Jan
Answer: C: 3-Jan 
Explanation: Drinking water should be moderately hard. Softening of water is recommended when the hardness exceeds 3 mEq/L (300 mg per litre).