Improperly treated human waste is a major source of environmental pollution
...leading to problems for both other humans and the environment as a whole. Pollution of rivers and streams by untreated or inadequately treated municipal and industrial effluents can render the watercourses unsuitable for use as sources of irrigation water and damage aquatic ecosystems.

The reuse of municipal wastewater for irrigation in the peri-urban zones of many developing country cities
...has both positive and negative impacts. The recycled water and nutrients are important for water conservation, but the health risks are significant unless there are tight controls. Not only are the farmers themselves exposed to high risk from pathogens, but their produce is then exported to a wider public who may also suffer.