| Class | Cause | Example |
| Waterborne | Pathogens that originate in fecal material and are transmitted by ingestion | Cholera, typhoid fever |
| Water-washed | Organisms that originate in feces are transmitted through contact because of inadequate sanitation or hygiene | Trachoma |
| Water-based | Organisms that originate in the water or spend part of their life cycle in aquatic animals and come in direct contact with humans in water or by inhalation | Schistosomiasis, Legionellosis |
| Water-related | Microorganisms with life cycles associated with insects that live or breed in water | Yellow fever |