Step 1: Understand the contributions of the individuals.
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Rajendra Singh is known as the 'Water Man of India' for his work in water conservation and rainwater harvesting, particularly in Rajasthan. His efforts have revived many water bodies.
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Bindeshwar Pathak is known for his work in sanitation and the creation of the Sulabh Shauchalaya.
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J.C. Chaudhry is a well-known educationist, not associated with water conservation.
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Sunderlal Bahuguna was an environmentalist famous for his involvement in the Chipko movement but not specifically for water conservation.
Step 2: Conclude.
Thus,
Rajendra Singh is known as the 'Water Man of India'.