There are many causes for water pollution but two general categories are - direct and indirect contaminant sources.

Direct sources include pollutants from factories, refineries, waste treatment plants etc. Indirect sources include pollutants that enter the water supply from soils/groundwater systems (fertilizers and pesticides) and from the atmosphere by rain water.

Direct contamination sources are easy to control by amendment of strict laws that polluted water is not disposed off directly into rivers and lakes, water treatment plants should be installed at industrial level.