This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Environment and health, Subject name: Social & Preventive Medicine
Purest water is 
Select and explain. 
A. River water, B. Rain water, C. Deep well, D. Impounding reservoir
B: Rain water
Answer: B: Rain water 
Explanation: Rainwater by nature is purest and soft. it gets contaminated when passing through the atmosphere by dust and microorganisms Park's Textbook of Preventive and Social Medicine, 25th edition, Page No. 767