This training manual is available in English and Spanish. The intended audience includes environmental health specialists, and professionals responsible for operation and maintenance of water supply systems. It has been designed to raise their level of training and to make maximum use of the scarce resources available for this type of activity. The manual will greatly help the implementation of training activities and will be an important tool for trainers in the design, preparation and carrying out of training courses on leakage control. At the end of the course, experienced participants should be able not only to repeat the training course with other professionals, but also to help water agencies in the formulation and implementation of a leakage control program. Leakage is one of the crucial issues to be dealt with in order to improve the efficiency and effectiveness of water supply services. Although the techniques and institutional aspects involved in a leakage control program are well known, appropriate materials for use in training programs on this problem are lacking. This training manual aims to fill this gap. Its use should be viewed as part of an overall strategy for the promotion of sound operation and maintenance (O&M) practices in the context of a comprehensive approach to institutional development.