Answer:
Louis Pasteur was the scientist who confirm that bacteria and other microorganisms is the reason for variety of diseases.
It gets polluted from fertilizers or any spilled chemicals. And those chemicals get obsorbed into the ground. And the gravity pushes them deeper in the soil, till it reaches the underground water (or aquifer)
concise verbal or mathematical statement of a relation that expresses a fundamental principle of science, like Newton's law of universal gravitation.