This book, available in English and Spanish, provides a practical guide to improving the performance of water treatment plants. The intended audience includes environmental health specialists, public health professionals, students, and workers including those who are responsible for designing, operating, maintaining or upgrading water treatment plants as well as managers of water agencies. The principles and ideas presented have been shown to be effective in increasing the capacity of water, and are based on extensive experience in upgrading a variety of treatment plants throughout the world. The procedures proposed apply not only to the optimization of existing treatment plants but also to the design of new ones.