Contamination of drinking water sources by sewage can occur from raw sewage overflow, septic tanks, leaking sewer lines, land application of sludge and partially treated waste water. Sewage itself is a complex mixture and can contain many types of contaminants. The greatest threats posed to water resources arise from contamination by bacteria (E-Coli, Coliform), nitrates, metals, trace quantities of toxic materials, and salts.
Sewage can be intentionally discharged to waterways through pipes or open defecation, or unintentionally during rainfall events. When humans use these waterways for drinking, bathing or washing, they are exposed to the associated pathogens, many of which can live for extended periods of time in aquatic environments. Humans then become ill by ingesting contaminated water, by getting it on/in skin, eyes or ears, or even from preparing foods with contaminated water. Sometimes humans can even become ill from inhaling contaminated water droplets.
Life-threatening human pathogens carried by sewage include cholera, typhoid and dysentery. Other diseases resulting from sewage contamination of water include schistosomiasis, hepatitis A, intestinal nematode infections, and numerous others. WHO estimates that 1.5 million preventable deaths per year result from unsafe water, inadequate sanitation or hygiene.
