Ensuring Excellence in Pharmaceutical Water Systems - Points to Consider

Ratul Saha, Ph.D. Director, Global Sterility Assurance Programs Bausch & Lomb

Introduction

Water plays a critical role across the pharmaceutical industry—as a raw material, inactive ingredient, processing aid, and vehicle for medicinal products. It is essential in the formulation and manufacture of dosage forms, active pharmaceutical ingredients (APIs), API intermediates, compendial articles, analytical reagents, and cleaning processes (USP <1231>).

Given its extensive use, maintaining appropriate water quality is vital for both sterile and non-sterile medicinal products. To ensure this, water treatment and distribution systems must be properly designed, constructed, installed, commissioned, qualified, monitored, and maintained. These systems should consistently deliver water of suitable quality while minimizing the risk of microbiological contamination (EU Annex 1, 2022).

Pharmaceutical manufacturing utilizes various grades of water, each tailored to specific applications. This article focuses on high purity water systems (HPWS) - specifically Purified Water and Water for Injection (WFI) - with an emphasis on microbiological considerations.

Achieving the required water quality demands careful attention to multiple variables throughout the design, control, monitoring, and maintenance of HPWS. Among these, source water quality stands out as a critical determinant. It directly influences the effectiveness and reliability of the system, making it a foundational element in ensuring microbiological integrity and compliance.

According to USP<1231> Source Water is the water that enters the facility. The chemical and microbial attributes of the starting source water are fundamentals and important to determine the design of the pre-treatments of the HPWS to remove or reduce the impurities in order to meet the finished water specifications. The source water should meet the drinking (i.e., potable water) water standards set by different agencies across the globe. World Health Organization (WHO) considers that “drinking-water” should be “suitable for human consumption and for all usual domestic purposes including personal hygiene.” Diverse regulatory agencies adopt similar definitions. According to US EPA, Heterotrophic microorganisms are a broad, diverse group, including bacteria, yeasts, and molds, that require organic carbon for growth. Heterotrophic plate count (HPC) is a procedure for estimating the number of live, culturable heterotrophs in a water sample. HPC monitoring can give an indication of the general quality of water in the distribution system; a significant increase in HPC numbers can indicate a potential water quality problem. A reasonable maximum bacterial action level for source water is 500 Colony Forming Units (CFU)/mL. Higher levels of HPC bacteria (>500 CFU/mL) can cause interference in the detection of other microorganisms that could be present in a water matrix, including indicator organisms (e.g., coliform bacteria). Elevated HPC concentrations may be a sign of more biologically active water. Biologically active water can be caused by many factors, including low disinfectant residual and/or high nutrient concentrations. These are the types of conditions that allow opportunistic pathogens to grow and flourish (US EPA). Seasonal variations in temperature, growth of flora and residual disinfectant levels may also cause fluctuations in microbial content of source water. Monitoring should be frequent enough to cover these variations.

The characteristics and profile of the source water should guide the robust design of a HPWS. Depending on the initial water quality and the required specifications of the final product, system configurations may vary. However, typical components involved in HPWS generation include:

• Multimedia filters, pre-filters, softeners, and activated carbon filters
• Ultraviolet (UV) disinfection, Reverse Osmosis (RO), and Continuous Electro deionization (CEDI)
• Ultrafiltration or distillation for producing Water for Injection (WFI)
• Distillation or heat exchangers may be employed to generate hot Purified Water when stringent microbial control is necessary

Given the limitations of UV technology, its placement within the system should be strategic to maximize microbial and Total Organic Carbon (TOC) reduction. Microbial retentive filters may also be integrated into the generation system, but selecting the appropriate pore size is essential - particularly to mitigate risks posed by waterborne Gram-negative organisms.

Regular maintenance and timely replacement of filtration components are crucial, as filters are susceptible to biofouling. For detailed guidance on water system design and control, USP <1231> serves as a valuable reference.

Biofilms are a major risk in pharmaceutical water systems due to their resilience, contamination potential, and difficulty in detection and removal. Pharmaceutical water systems must maintain extremely high purity standards, and biofilms pose a serious threat to this integrity.

Biofilms

A biofilm is an assemblage of surface-associated microbial cells that is enclosed in an extracellular polymeric substance (EPS) matrix. It can exist as a Colony (Single Species) or Community (Multi Species). In other words, biofilms are alive and have a complex social structure, a structure that both protects them and allows them to grow. It can also be defined as, a biofilm is a collection of organic and inorganic, living and dead material collected on a surface. It may be a complete film or, more commonly in water systems, small patches on pipe surfaces. Biofilms in drinking water pipe networks can be responsible for a wide range of water quality and operational problems. Biofilms can be responsible for loss of distribution system disinfectant residuals, increased bacterial levels, reduction of dissolved oxygen, taste and odor changes, red or black water problems due to iron or sulfate-reducing bacteria, microbial-influenced corrosion, hydraulic roughness, and reduced materials life (Characklis and Marshal, 1990). Low level of nutrients in pharmaceutical water systems might make the environment prone to biofilm formation. Collectively, the design of the system, materials of construction of pipework, the diameter and bends of piping, rate of flow along with maintenance of the system play a role in biofilm control.

Some of the key learnings from biofilms are:

• EPS is known as the ‘Dark Matter’ of biofilms.
• Corrosion can lead to biofilm formation.
• Biofilm can lead to microbial induced corrosion.
• Surface type and conditions plays a role.
• System design, validation and monitoring are critical.
• Data analysis and trending is important (not only bioburden but TOC and conductivity are equally important). System with low TOC (e.g., <20 ppb) are less conducive for biofilm formation.
• Timing is critical.
• Both killing and removal of biofilm is equally important.
• Adherence to robust PM is critical.
• Traditional microbiological test might underestimate the actual bioburden in a system for several reasons such as Viable but Non-culturable Cells (VBNC); Sampling methodology and techniques challenges; biofilm growth pattern.

Points to Consider for the Design, Operation and Maintenance of HPWS:

• Manufacturing site should maintain a level of expertise in the area of water generation and maintenance. The development of a specific water training plan should be implemented to support this. Regular scheduled reviews by a panel of multidisciplinary water specialists should be arranged where any planned water changes or issues can be discussed and reviewed. At the minimum Subject Matter Expert (SME) from the following departments (facilities, QC microbiology, manufacturing) should be part of the multidisciplinary team.
• The water system should be designed such that the generated purified water and WFI at the minimum conforms to Purified Water and WFI, USP<1231> recommendations and EU pharmacopeial requirements. It is important to note from the very beginning that Ambient systems are more prone to microbial attachment and proliferation.
• The quality of the source/raw water input to the water system as per the USP requirement should be potable as per national standards:
  • European Directive 98/83/EC
  • U.S. National Primary Drinking Water Regulation (NPDWR) from the Environmental Protection Agency
  • World Health Organization (WHO)

• For optimal performance, the design and operation of the water generation system (Purified or WFI) should be based on a comprehensive feed water analysis of the potable water supply which will be unique to each respective site.
• A comprehensive and well-structured risk assessment should serve as the foundation for determining the system’s design, operational strategy, sampling plan, and preventive maintenance program.
• Where the purified water generation system requires a reverse osmosis process, the max allowable parameters for RO feed water should be met. Adequate RO membrane and model type should be selected compatible with cleaning and sanitization agents.
• For example, RO units used for the production of compendial waters should use pharmaceutical grade, loose wrap, or full-fit elements which are spiral wound with a thin film composite design. The choice to membrane could be polysulfone on a polysulfone support matrix.
• The requirement for a sodium hypochlorite pre-treatment will depend on the quality of the potable water supplied to the site. Manufacturing Sites must have a knowledge of the chlorine levels present in the water in order to determine whether this pretreatment is required. The purpose of the sodium hypochlorite pre-treatment is to ensure that there are sufficient levels of chlorine present in the water for microbial control. Any additional chlorine injection should be adequately controlled and monitored, and neutralized as chlorine could impact RO membrane.
• Within water system multi-media filters perform an essential function of removing silt and particulate matter from the potable water. Backwashing of multi-media filters is required to re-stratify the layers of the multi-media filters and for filter maintenance and should be controlled automatically where possible. The backwashing of the filters also aids in maintaining microbial control of the water system.
• The requirement for organic scavengers will depend on the quality of the potable water supplied to the site. Sites must have knowledge of the levels of organics present in the water in order to determine whether organic scavengers are required. The purpose of organic scavengers is to protect the downstream Reverse Osmosis (RO) and Continuous Electro-De-Ionization (CEDI) membranes from organic fouling through the removal of naturally occurring organics in the water. Regeneration of the organic scavengers is required to remove the organics filtered from the water to maintain the resin integrity and should be controlled automatically where possible.
• The purpose of water softeners is to remove calcium and magnesium from the water to prevent scaling of the downstream RO and CDI membranes. Regeneration of the softeners is required to remove the minerals filtered from the water to maintain the resin integrity and should be controlled automatically where possible.
• The purpose of the carbon filters is to strip the water of chlorine and other organic contaminants as these can be harmful to the downstream RO and CDI membranes hence the presence of carbon filters improves the performance of the water system. Sites must have knowledge of the levels of chlorine and other organics and determine the number of carbon filters required based on the feed water characteristics.
• Preliminary filtration with an appropriate filter upstream of the RO unit is required to filter any particles present in the water therefore protecting the RO unit. Sites must have knowledge of the size and level of the particles and determine the prefiltration requirements based on the feed water characteristics.
• Based on the feed water characteristics the manufacturing sites must determine if preliminary UV disinfection upstream of the RO unit is required to aid in microbial and TOC control.
• Break tank must be in place on the RO Skid. The purpose of a break tank is to provide an atmospheric break for water re-circulated from the downstream RO and CDI units.
• The RO unit performs the essential function of water purification by passing the water through a semi-permeable membrane and removing contaminants such as dissolved solids, organics, pyrogens and microbes from the water. Based on the feed water characteristics and the quality of the water required the Sites must have knowledge and determine if a single pass or double pass RO unit is required. A double pass RO is preferred to aid in enhanced microbial control. Point to note-Systems that maintain total organic carbon (TOC) levels below 20 ppb after reverse osmosis (RO) have demonstrated superior microbial control.
• The requirement for a degasser in the water system will depend on the quality of the potable water supplied to the site. Sites must have a knowledge of the levels of carbon dioxide present in the water in order to determine whether a degasser is required. The purpose of the degasser is to strip the permeate of carbon dioxide which enhances the performance of the CDI unit.
• The purpose of the CDI unit is to remove dissolved ions to produce high quality water. The quality of the water output from the CDI should be automatically monitored. In the event that the water does not meet quality requirements as per compendia, it should be directed to drain until an intervention can be carried out to resolve the issue.
• For ambient system post CDI Filtration, a 0.1μM filter could be used to facilitates the removal of any remaining microbes from the water. Sites must verify that they are suitable for their intended application, use period, and use process, including flow rate. The frequency with which the filter is to be changed should be based on data generated during the validation of the system.
• The final UV Disinfection is required for microbial control. UV should be strategically placed to obtain the benefit of microbial and TOC reduction. If only used for TOC reduction, the appropriate wavelength should be selected and used. UV lights must be properly maintained to work. The glass sleeves around the bulb(s) must be kept clean on their effectiveness will decrease. In multi-bulb units there must be a system to determine that each bulb is functioning.
• A tank fabricated from stainless steel is required for the storage of purified water and WFI. Rupture disk failures should be detected through an alarm device. The interior surface of the tank should be smooth. There should be ability to spray the tank headspace using spray balls on recirculating loop returns and of which coverage testing has been performed, use heated, jacketed/insulated tanks which will aid in control of corrosion and biofilm formation. The vent filter should be located in a position on the holding tank where it is readily accessible and should also be tested for integrity.
• Traditional diaphragm valves should be replaced with zero dead leg diaphragm valves for existing traditional system and zero dead leg valves should be used for newly designed or repaired/renovated system. Valves should have smooth internal surfaces. Valve installation should promote gravity drainage. (Note: The ball valves are not considered sanitary valves since the center of the valve can have water in it when the valve is closed. This is a stagnant pool of water that can harbor micro-organisms and provide a starting point for a biofilm).
• Distribution system configuration should allow for the continuous flow of water in the piping by means of recirculation. Use of no recirculating, dead-end, or one-way systems or system segments should be avoided whenever possible. There should be proper sloping to avoid water stagnation. There should be no threaded fittings in the water system. All pipe joints must utilize sanitary fittings or be butt welded. Stainless Steel plumbing and piping is preferred over plastics as materials of construction.
• Although this topic remains debatable, it is generally accepted in the industry that turbulent flow tends to inhibit biofilm formation or reduce the likelihood of biofilms shedding bacteria into the water. Therefore, pumps and systems should be designed to achieve and maintain fully turbulent flow conditions. It is essential to document and monitor these turbulent flow conditions, which also promote effective heat distribution and uniform dispersal of chemical sanitizing agents (To learn more about turbulent flow refer to USP<1231>). According to EU Annex 1, the flow rate should be established during qualification and be routinely monitored.
• If redundant components, such as pumps or filters, are used, they should be configured and used and maintained to avoid microbial contamination of the system.
• Heat exchangers should be constructed to prevent leakage of heat transfer medium into pharmaceutical water and for heat exchangers designs where prevention may fail there should be a means to detect leakage (monitor pressure differentials). When not in use, heat exchangers should not be drained of the cooling water. Cleanability of the heat exchanger should also be considered during the design. Pumps should also be of sanitary design with seals that prevent contamination of water. Double-sheet tube type heat exchangers are recommended. (To learn more about Heat Exchangers refer to US FDA Inspection Technical Guide-Heat Exchangers to Avoid Contamination.)
• Microbial control in water systems is achieved through sanitization practices. System should be routinely sanitized by thermal or chemical means. Thermal approaches to system sanitization include periodic or continuously circulating hot water and the use of steam. Temperatures of 65°–80° C are most commonly used for thermal sanitization. Continuously recirculating water of at least 65° C (EU Annex 1 suggests constant circulation temperature above 70° C if produced by distillation) at the coldest location in the distribution system also has been used effectively in stainless steel distribution systems when attention is paid to uniformity and distribution of such self-sanitizing temperatures. The frequency should be defined based upon the overall system design, validation and should be supported by results of system microbial monitoring to prevent biofilm formation. The routine frequency of sanitization should be established in such a way that system operates in a state of microbiological control and does not regularly exceed Alert and Action Levels. Heat distribution study is critical to ensure adequate thermal sanitization. Hot systems (self-sanitizing) are less prone to microbial survival, attachment and proliferation.
• Validation of thermal methods should include a heat distribution study to demonstrate that sanitization temperatures are achieved throughout the system, including the body of the use point valves, sampling ports, instrument side branches and fittings, couplings and adapters, relying on water convection and thermal conduction through system materials for heat transfer to wetted surfaces.
• Validation of chemical sanitization should demonstrate adequate chemical concentrations throughout the system, exposure to all wetted surfaces including the body of use point valves, and complete removal of the sanitizing agent from the system at the completion of treatment.
• HPWS should include continuous monitoring of Total Organic Carbon (TOC) and conductivity. This will give a better indication of overall system performance than periodic sampling. Justification for placement of instruments should be based on risk.
• Both Process Control (PC) and Quality Control (QC) sampling are equally vital components of a robust monitoring strategy. PC sampling offers critical insight into the overall health of the system and serves as a key tool for investigating excursions and identifying root causes. Effective trend analysis, coupled with timely discussion and communication of trend data, is essential for proactive system management.
• Ensure bioburden method can recover microorganisms of interest such as microorganisms of concern and objectionable organisms. Microbial identification of recovered isolates plays a pivotal role—not only in tracking trends but also in confirming the absence of microorganisms of concern or objectionable organisms, such as Burkholderia cepacia complex, Pseudomonas aeruginosa, Stenotrophomonas maltophilia and others. This ensures the system remains compliant and microbiologically safe.
• Hoses that are attached to points of use to deliver water must not chemically or microbiologically degrade the water quality. Hoses and valve extenders should be in a scheduled sanitization and preventative maintenance program. Hoses and valve extenders should be completely drained and dried after each use and stored in a vertical position to avoid microbial proliferation and biofilm formation.
• Flushing shears off fragile biofilm structures growing on surfaces within the valve and water path. Flushing should not only be performed prior to sampling and use of the water for manufacturing processes but flushing should also be performed at a defined frequency for point of use ports not in use or infrequently used (e.g., during out of service, maintenance, repair or during facility shutdown periods). According to USP<1231>, a fully open valve flush (at >8 ft/s velocity within the valve and connector) for at least 30 s typically provides sufficient shear forces to adequately remove any fragile biofilm structures but it would be prudent to validate the flushing time or volume as each system is unique.
• Routine walk through of the water system should be performed to detect leaks or malfunctioning. Leaks should be repaired in a timely manner to prevent ingress of exogenous contamination.
• Exogenous microbial contamination of bulk pharmaceutical water comes from numerous possible sources. Care should be given to sampling, testing, system design, and maintenance to minimize microbial contamination from exogenous sources. Sequence of valve opening is another critical factor to prevent exogenous contamination of the system.
• Appropriate Disruption Recovery/Return to Service procedure with adequate Change Control Process and Practices. Often an oversight leading to microbial issues and system failures.
• One of the most critical aspects of maintaining a state of control of pharmaceutical water system from microbial control standpoint is to have a robust preventative maintenance (PM) program.

Points to Consider for a Robust PM Program

• There should be regular preventative maintenance including passivation (Stainless Steel Based System) and chemical sanitization scheduled for the water systems to ensure the integrity and quality of the system is maintained. A record of any interventions or maintenance performed should be kept.
• Review Operations Log.
• Training staff in servicing equipment to reduce failure rate.
• Inspect entire system and related points.
• Report and forecast potential issues and resolve in advance of failure.
• Communicate actions needed and consequences if no action is taken.
• Test water quality for each piece of equipment.
• Replace reverse osmosis (RO) membranes.
• Replace RO pre-filter.
• Replace post-filter.
• Review Passivation (Stainless Steel) frequency and record.
• Perform Passivation as per schedule.
• Ensure proper pump functionality.
• Record and monitor settings and working pressures.
• Inspect UV system for proper operation.
• Clean ultraviolet lights.
• Check RO system.
• Inspect tank level controls are in proper operation.
• Check proper operation of water softeners.
• Check proper carbon filter processes and operation.
• Check Proper multi-layer ML filter operational status and operation.
• Clean and inspect conductivity sensors.
• Prevent unexpected shutdowns as much as possible.
• Establish rouge inspection program for stainless piping and components.
• Replace valve diaphragms and gaskets per established schedule.

Conclusion

In conclusion, maintaining a robust pharmaceutical water system is essential for ensuring the quality and safety of medicinal products. High Purity Water Systems (HPWS), including Purified Water and Water for Injection (WFI), require meticulous and thoughtful design, validation, operation, and maintenance to prevent microbiological contamination (critically biofilm formation) and ensure compliance with regulatory standards keeping into perspective the intended use of the water. Source water quality plays a foundational role in system design and configuration, influencing the selection of pretreatment methods and purification technologies such as reverse osmosis, CEDI, and UV disinfection. A multidisciplinary approach involving facilities, microbiology, and manufacturing teams is critical for effective oversight. Continuous monitoring of key parameters like TOC and conductivity, strategic sanitization practices, and a comprehensive preventative maintenance program are vital to sustaining system integrity, thus preventing the risk of biofilm formation. Collectively, these measures support a state of control that safeguards product quality and patient safety-“Start Clean to Stay Clean”.

Disclaimer: This article reflects the views and opinion of the author and should not be construed to represent any company’s views or policies. My communication represents my own best judgment.

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