What is Pollution? Describe water pollution, its sources and effect on human health. (UPSC 2017, 15 Marks, )

प्रदूषण क्या है? जल प्रदूषण का वर्णन करें, इसके स्रोत और मानव स्वास्थ्य पर इसके प्रभाव। (What is Pollution? Describe water pollution, its sources and effect on human health.)