Based on the classic text by Fair, Greyer, and Okun, this new edition has been completely revised and updated including eight completely new chapters by university professors and engineers practicing in the field. It reflects current practice, includes access to an academic version of the commercial software Haestad Methods Water Solutions by Bentley, and now includes homework problems. This is a time of mounting urbanization and industrialization and resulting stress on water and wastewater systems. Clean and ample sources of water for municipal uses are becoming harder to find and more expensive to develop. Effective design and efficient operation of engineering works ask, above all, for a fuller understanding and application of scientific principles. The results of scientific research are being incorporated with remarkable success in new designs using both U.S. and SI systems equations, examples and problems as well as new operating procedures. This classic text, now updated, grounds readers in both the science and art of water and wastewater engineering that global engineers need to service their customers and communities.