Water and steam are used in the manufacture of products, cleaning operations, and laboratory activities within pharmaceutical or biopharmaceutical operations. Systems that generate and distribute water and steam that may come into contact with product/or process contact surfaces or used in product testing are subject to Commissioning and Qualification (C&Q) (verification). Water can also be a final product, for example, as a pharmacopeial water and as part of a combination product. This Guide addresses pharmaceutical water and steam systems C&Q by both science and risk-based as well as traditional approaches to increase understanding of GMP water and steam systems in the pharmaceutical and biopharmaceutical industries. It is intended to assist in the integration of the capital project management process, the C&Q process, best practices for defining the PQ approach and the ongoing operation into the Quality Risk Management (QRM) validation lifecycle. The third edition of this Guide incorporates the general changes in C&Q approaches developed and instituted over the past 10 years. It contains chapters on process analytical technology and rapid microbial methods, and appendices covering process water, pure steam, and process steam, typical specifications, change management, and a sample turnover package. This Guide is aligned and can be used in conjunction with the ISPE Baseline® Guide: Volume 5 – Commissioning and Qualification (Second Edition), the ISPE Good Practice Guide: Good Engineering Practice (Second Edition), the ISPE Baseline® Guide: Volume 4 – Water and Steam Systems (Third Edition), and ISPE GAMP® 5: A Risk-Based Approach to Compliant GxP Computerized Systems (Second Edition).