This guide is intended for people involved in the management and operation of small- to mediumsized organized water supply systems. The content has been developed with particular consideration for operational-level personnel with responsibility for chlorination (for example, water treatment plant operators and technicians). The material presented within this guide may also be relevant for engineers and representatives from public health, local government, non-governmental organizations, as well as any other individuals supporting water safety planning activities for the supply of safe drinking-water. <br> <b>Part 1. Chlorination principles:</b> Describes key chlorination concepts, providing a knowledge foundation for the implementation of effective chlorination practices.<br> <b>Part 2. Chlorination practices:</b> Describes the practical application of the concepts presented in Part 1, including calculations and procedures for safe and effective chlorination of drinking-water supplies.