The world faces a grave water risk that affects all aspects of human life and ecology with implications for food security, energy production, industrial activity and human health. India is particularly affected as it has 16% of the world's population but access to less than 4% of global freshwater resources. In this study, we use mobile (moving) sensors to spatially and temporally map river water quality based on in-situ data gathered in some of India's major rivers. Data visualizations generated are intended to pinpoint sources of pollution, ensure regulatory compliance and examine health of the water body. We show that such cyber physical sensing techniques can be a powerful and more practical (or cost-effective) way to dynamically monitor, predict and regulate the quality of large bodies of water.