In this chapter, the author discusses a wide range of water contaminants, the sources of these contaminants, and their impact on drinking water supplies from both surface water and groundwater sources. Moreover, before moving on to an in-depth discussion of drinking water pollution and many of the contaminants involved, it is appropriate to highlight drinking water crises that have occurred in the United States. Non-point sources now comprise the largest source of water pollution, contributing approximately 65% of the contamination in quality- impaired streams and lakes. The main problem with respect to serious groundwater pollution has been human activities. When we improperly dispose of wastes or spill hazardous substances onto the ground, we threaten our groundwater and in turn public health. In fact, the amount of pollution being discharged from the plants has been cut by over one-third during the past several decades, even as the number of people served has doubled.