Water is an essential resource for human life. However, more than 1.2 billion people still do not have access to safe drinking water. Microbiological contamination is the primary cause of disease outbreaks with drinking water. This book presents research work, undertaken to determine the disinfection efficiency of ozone. Inactivation of pure and mixed culture of E. coli and Salmonella, inoculated in distilled water and drinking water samples was conducted under controlled environmental conditions such as pH, temperature, ozone dose and contact time to study their effects on disinfection efficiency of ozone. It is evident from the results that the disinfection is a rate process and is dependent upon the rates of reaction between the disinfectant and the microorganisms in water. Ozone disinfection efficiency was found to be higher at low pH and high temperature range. The book is especially useful to students and professionals dealing with drinking water disinfection technology or anyone else interested to study about the pathogens in drinking water.