ABSTRACT
THEORY AND APPLICATION There are many technical reasons for including storage systems in pharmaceutical water systems. In less complex distribution systems, a storage tank may simply provide a convenient method of repressurizing compendial water prior to a distribution loop. For other applications, such as Water for Injection systems with distillation, storage systems are required to provide an atmospheric discharge point for distilled product water and to maintain and allow the recirculation of hot Water for Injection at an elevated temperature, generally greater than 808C. While condensate receivers may also be used to collect distillation unit product water, the need for a storage tank is not eliminated due to the required recirculation of product water, generally at an elevated temperature to insure microbial control (FDA, 1986). For USP Purified Water systems, product water from single-pass or double-pass reverse osmosis (RO) unit, with or without polishing continuous electrodeionization (CEDI), may be slightly pressurized (10-30 psig). Without a storage tank for a USP Purified Water system, RO membranes will not tolerate rapid changes in the product water pressure associated with “point-of-use” draw-off, which, unfortunately, results in rapid loss of RO membrane integrity. As indicated earlier, a sound system design includes three loops: pretreatment, ion removal, and storage and distribution. There are several factors that demonstrate the technical superiority of system design, outlined in detail as follows:
l From a microbial standpoint, a dedicated storage system isolates the Purified Water or Water for Injection “generating” system components from the distribution loop. As discussed in previous chapters, it is extremely desirable to maintain total viable bacteria levels within the generating pretreatment section of the system at a value less than 500 cfu/mL (the suggested “Drinking Water” value in the General Information section of USP). Obviously, the 500 cfu/mL total viable bacteria level is significantly greater than typical Alert and Action Limits for Water for Injection. The 500 cfu/mL is also greater than “acceptable” total viable bacteria Alert and Action Limits for critical USP Purified Water applications, such as the production of topical solutions, antacids, inhalants, and ophthalmic solutions. Segregation of the water purification generating system from the storage and distribution system provides an air break with atmospheric pressure delivery of water from the water purification generating system to the storage and distribution system.
