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
Disinfection of water is not requihred if the source is from- 
Select and explain. 
A. Tube well, B. Step well, C. Draw well, D. River
A: Tube well
Answer: A: Tube well 
Explanation: Park's textbook of preventive and social medicine 23rd edition. *Tube wells are usually machine dug and may be several hundred metres deep. Deep wells furnish the safest water and are often the most satisfactory sources of water supply