As more water systems turn to safer alternatives to chlorine gas, the generation of hypochlorite on site has become increasingly common. M65, On-Site Generation of Hypochlorite, presents the principles of on-site generation (OSG), the differences between low-strength and high-strength OSG systems, and the subsequent impact each of these systems has on design, construction, and maintenance for water and wastewater utilities. M65 provides operators and engineering staff with a basic understanding of how to design and install both low- and high-strength OSG systems, how they work, and how they compare with other popular forms of chlorine currently on the market. A cost analysis and an examination of how OSG affects disinfection by-product formation are also included. This manual should help operators, planners, management, and engineers improve their decision-making processes about OSG systems using a holistic risk management approach that considers not only triple-bottom-line approaches but also the specific regional situation when choosing a chlorination system.