Water can be contaminated by physical, chemical, biological, and radiological contaminants.
Physical contaminants are those contaminants that impact the physical appearance of physical properties of water Like sediments, suspended organic matter, etc.
Chemical contaminants can be found in the form of elements as well as compounds.
They can be natural or manmade. eg. nitrogen, salt, pesticides, fertilizers, bleach, metals, toxins, human or animal waste, drugs, etc.
Biological contaminants are referred to as living microorganisms or microbes present in water like bacteria, viruses, protozoa, and parasites.
Radiological contaminants are basically chemical elements with unbalanced protons or neutrons which makes the atoms unstable enabling it to emit ionizing radiation.
Caesium, uranium-plutonium are some of the radiological contaminants.