Hazardous substances are emitted to water bodies both directly and indirectly through a range of diffuse and point source pathways. Hazardous materials, include, without limitation, synthetic organic chemicals, petroleum products, heavy metals, radioactive or infectious materials. 

A range of measures can be implemented to reduce the emissions of hazardous substances to water. It encompasses product substitution, restrictions on marketing and use, requirements to demonstrate the implementation of clean production processes and best available techniques in applications for industrial permits, fiscal instruments, the setting of emissions and environmental quality standards, and action to raise public awareness.