2.2 Diseases associated with water
The majority of water-related health problems are caused by infectious agents that can invade the body and cause disease. They include pathogenic (disease-causing) bacteria, viruses, protozoa and parasites. Infectious agents can cause disease when they are ingested (eaten or swallowed) or otherwise come into contact with the human body. The different ways in which water is involved in this contact can be used to classify the diseases into four main groups: waterborne, water-washed, water-based and water-related diseases.