Quality of water for dialysis has become a central issue for safety and “Good Dialysis Practice”. When considering clinical sequelae and related patient well-being, “water quality” is to date considered a topic with a similar level of importance like blood compatibility of the extracorporeal dialysis circuit. This textbook addresses key factors and conditions which describe and determine water purity. Detailed information is given about chemical and biological purity of such fluids and their possible toxicological and physiological consequences. Further, answers to questions such as “How to prepare ultrapure fluids for dialysis?” and “How to perform a system validation?” or “How to set standards for the monitoring of water purity?” are given. Safety aspects for water treatment facilities and responsibilities to be taken by the dialysis centre staff, as well as actual normative prescriptions from national and international (ISO)-norms complement the scope of this book. The approach suggested by the authors in this textbook considers, thus, all steps of the “water purification cascade”. The result is a comprehensive handbook with state-of-the-art knowledge, clinical operational insight gained from Fresenius’s 3000 plus clinics and recommendations for day-to-day clinical practice. Accordingly, this book may have its impact as a water quality management guide. The authors of this textbook are renowned specialists with proven records of experience both in water treatment modalities and as employees of the dialysis industry.