The hydrosphere refers to all water on the earth's surface. Human activity has severely polluted the hydrosphere over the span of many decades. Polluted water impacts human health in many ways.

• About one billion people per year will become sick from polluted water (which includes wastes such as metals)
• Pathogens in polluted water spread illnesses such as Legionnaire's disease and cholera
• Chemical pollutants such as lead or arsenic may cause health problems, including cancer
• Polluted water may also cause skin rashes, eye infections, and respiratory infections