A pathogen is a disease-causing microorganism found in water, including bacteria, viruses, protozoa, and helminths. Waterborne pathogens are a leading cause of illness and death worldwide.
Waterborne pathogens are microorganisms capable of causing disease in humans and animals when transmitted through contaminated water. Major categories include bacteria (such as Salmonella, Vibrio cholerae, and pathogenic E. coli), viruses (such as norovirus, rotavirus, and hepatitis A), protozoa (such as Giardia lamblia and Cryptosporidium parvum), and helminths (parasitic worms such as Schistosoma). The World Health Organization estimates that contaminated drinking water causes over 500,000 diarrheal deaths annually, primarily in developing countries. Waterborne pathogens enter water supplies through human and animal fecal contamination, including sewage overflows, agricultural runoff, and inadequate sanitation. Water treatment processes such as coagulation, filtration, and disinfection with chlorine, ozone, or ultraviolet light are designed to inactivate or remove pathogens. Cryptosporidium is particularly challenging because its oocysts are resistant to chlorine disinfection, requiring filtration or UV treatment for effective removal. Multi-barrier approaches to drinking water safety, from source water protection to treatment to distribution system management, are considered the most reliable strategy for preventing waterborne disease outbreaks.