Disinfectants play a crucial role in water treatment by inactivating harmful microorganisms to ensure safe drinking water. Common disinfectants used include chlorine gas, sodium hypochlorite, calcium hypochlorite, chloramines, chlorine dioxide, ozone, and UV light. Chlorine is widely applied due to its effectiveness, though chlorine dioxide, ozone and UV are also effective against resistant microbes. Chloramines provide residual disinfection in distribution. Water quality, pH, contact time, residual levels, and disinfection byproduct formation must be considered when selecting a disinfectant. Cost and maintenance requirements also factor into the decision. Proper disinfection is essential for destroying waterborne pathogens and protecting public health through production of microbiologically safe drinking water.