The harmful substances like sewage, toxic materials, silt etc., when gets mixed with water, causes water pollution. The pollutants which cause water pollution are the chemical waste from industries, sewage, silt, agricultural chemicals and garbage thrown into water.
Water gets polluted in the following ways:
1. Water can be contaminated by human waste or sewage.
2. Industries such as oil refineries, paper factories, textile and sugar mills and chemical factories discharge harmful chemicals into rivers and streams. These chemicals include arsenic, lead and flourides.
3. Some industries and power plants releases hot water into the rivers. Hot water can also be considered as a pollutant.
4. The excessive use of pesticides and fertilizers in agriculture also causes water pollution.