How do untreated sewage and industrial waste harm water quality?

Untreated sewage and industrial waste significantly degrade water quality by introducing harmful substances that disrupt aquatic ecosystems and threaten public health.1

Domestic Sewage

Domestic sewage is a primary source of pathogens, which pose direct risks to human health. It also contains putrescible organic matter that increases the biochemical oxygen demand (BOD). As microorganisms decompose this organic material, they consume dissolved oxygen, which can lead to oxygen-depleted or septic conditions that kill fish and other aquatic life. Furthermore, sewage introduces nitrates and phosphates, which trigger algal blooms and accelerate eutrophication, ultimately causing the premature aging and death of water bodies.23456

Industrial Waste

Industrial waste introduces specific, often toxic, chemical compounds and heavy metals that can poison aquatic organisms and cause long-term health issues in humans. Some industrial chemicals increase water acidity, making it corrosive enough to destroy living organisms. Additionally, many facilities discharge heated water, which reduces dissolved oxygen levels and further stresses aquatic environments. Persistent pollutants, such as polychlorinated biphenyls (PCBs), can accumulate in the food chain, posing severe, long-lasting hazards to both wildlife and humans.1783