Distillation, using Vapor Compression (VC) or Multi-Effect (ME) stills, is the method of choice as the Final Treatment for the production of WFI. On the other hand, there are numerous configurations of USP Purified Water systems. While the majority is Reverse Osmosis/Ion Exchange based, a significant number of installations utilize distillation. Without exception, proper Pretreatment is an essential building block of every water system. In addition to economics, a pretreatment system design is influenced by two main considerations: 1) Final Treatment choice: VC, ME, or RO/Ion Exchange. 2) Contaminants in the raw water. The paper presents case studies of systems that utilize distillation as well as membranes for the Final Treatment step, and shows the corresponding suitable pretreatment, which may include: · Multi-media filtration · Softening for hardness removal · Carbon filtration · Polishing softening for ammonia removal · Reverse Osmosis · Ultra-Violet light

Raw water, which must meet EPA “Drinking Water Standards”, or equal Japanese or European Standards, is normally treated with chlorine or chloramine as disinfectant. These disinfectants must be removed in the pretreatment steps, · in order for the product water to meet the USP requirements for conductivity and TOC · to protect against membrane failure, and the corrosion and Stress Corrosion Cracking of stainless steel equipment. The paper shows options for the removal of both disinfectants. The paper delineates the specific application, the rationale behind certain choices, and the associated system economics. The paper also provides comparisons and consideration factors relevant to the choice of Pretreatment and Final Treatment systems.