The aim of this manual is to be a useful tool for anyone who will deal with the design of urban water supply and sanitation in the developing countries. The practical design calculation, tables, figures, and graphs are meant to provide an instrument for design engineers to take initiatives in designing urban water supply and sanitation system. Although the field of water and sewage treatment offers a variety of technological choices, only few of them in principle fully meet the specific requirements of developing countries in this treatise few of those technologies are picked up and their design criteria and model design calculations are presented.