There are many different sources of water accessible to humans. It is this variety that allows humans to inhabit almost every corner of the planet. These sources include lakes, rivers, creeks, natural springs, aquifers, manmade dams, and oceans. Each source of water, due to its different location, has different concentrations of substances including contaminants. Water can gather these substances at various stages of its cycle due to various factors including the characteristics of surrounding water bodies (freshwater running into the ocean), the catchments and land that the rain falls within, and the type and frequency of interactions with biological processes and humans. Figure 11.1 presents a “life cycle” for contaminants, contamination sources, treatment methods, and potential health concerns.