Frequently Asked Questions

ANSI/AAMI ST108:2023 is the American National Standard for water used in the processing of medical devices. It establishes minimum requirements for water quality at different stages of medical device processing, including cleaning, rinsing, disinfection, and sterilization. The standard helps healthcare facilities determine what type of water is appropriate for each processing step and how to verify that the water continues to meet the required specifications.

ST108 matters because water quality can directly affect cleaning effectiveness, medical device condition, sterilization-related processes, and patient safety. The standard recognizes that water impurities can contribute to corrosion, pitting, scaling, biofilm buildup, increased microbial load, endotoxin concerns, reduced cleaning agent performance, equipment degradation, and indirect patient risks such as infection, toxicity, and pyrogenic reactions.

Source within ANSI/AAMI ST108:2023: Foreword, Introduction, Clauses 1.1, 1.2, 5.1, 5.2.1.

ANSI/AAMI ST108 was created to provide clearer, more specific requirements for the water quality and steam purity needed to effectively process medical devices. The standard replaces AAMI TIR34 and moves the industry from technical guidance toward an American National Standard focused on minimum water quality requirements, water treatment, monitoring, maintenance, and quality control.

The need for ST108 is tied to the growing complexity of reusable medical devices, including devices with lumens, hinges, crevices, and other difficult-to-clean areas. The standard also recognizes that validated device processing instructions may not be fully effective if the water used during processing does not meet the quality required for the task. In simple terms, the right cleaning process still depends on the right water.

Source within ANSI/AAMI ST108:2023: Foreword, Introduction, Clauses 1.1 and 1.2.

A good first step is to form or formalize a multidisciplinary water management team. ST108 identifies this team as responsible for developing, implementing, and documenting the applicable requirements of the water management program. The team should include the people who understand how water is used in medical device processing and the people who establish, maintain, and monitor the water treatment system.

From there, facilities should assess their current water sources and points-of-use, determine which processes require Utility Water, Critical Water, or steam, compare current water quality results against ST108 specifications, and identify any gaps in equipment, testing, documentation, maintenance, or corrective action procedures. ST108 also recommends a risk analysis prior to water system installation and periodic review of the resulting evaluation plan.

Source within ANSI/AAMI ST108:2023: Clauses 4.1, 4.2, 4.3, 5.1, 6.2, 8.4.1, 9.1, 10.4, Tables 1, 2, 5, and 6.

ANSI/AAMI ST108:2023 is the first edition of the American National Standard for water used in the processing of medical devices, and it revises and replaces AAMI TIR34. A Technical Information Report, such as TIR34, provides technical guidance. ST108 establishes minimum requirements for water quality and steam purity necessary to effectively process medical devices intended for patient use.

In practical terms, ST108 gives healthcare facilities a more formal and structured standard for selecting water quality, qualifying water treatment and delivery systems, monitoring water quality, maintaining systems, and managing water quality through a multidisciplinary program.

Source within ANSI/AAMI ST108:2023: Foreword, Clauses 1.1 and 1.2, Bibliography reference [1].

ANSI/AAMI ST108 defines three categories of water quality for medical device processing: Utility Water, Critical Water, and steam. Utility Water is generally used for flushing, washing, and intermediate rinsing. Critical Water is used for higher-risk steps, including the final rinse after high-level disinfection, the final rinse for critical devices before sterilization, and feedwater for process steam production. Steam is vaporized water produced by a centralized boiler, generator, or heat exchanger and evaluated as condensate against defined criteria.

The standard is clear that tap water should not automatically be assumed to meet Utility Water requirements. Tap water may require treatment at the facility to meet the water quality values identified in ST108.

Source within ANSI/AAMI ST108:2023: Clauses 3.21, 3.76, 3.77, 3.85, 3.90, 6.2, Table 2, Annex A.1.

Hospitals can move toward ANSI/AAMI ST108 compliance by developing a water management program that defines responsibilities, identifies water quality requirements, verifies water quality at the point-of-use, and establishes routine monitoring, maintenance, documentation, and corrective action processes. Compliance is not simply a matter of installing water treatment equipment. It requires an ongoing program that demonstrates the water used in medical device processing is appropriate for the process and remains within specification over time.

Key steps include forming a multidisciplinary team, mapping water sources and points-of-use, determining where Utility Water, Critical Water, and steam are required, testing water against ST108 criteria, qualifying the water treatment system, setting alert and action levels, maintaining records, and responding when results are outside acceptable limits.

Source within ANSI/AAMI ST108:2023: Clauses 1.2, 4, 5.1, 6.2, 8.4.1, 9.1, 10.2, 10.4, 11.2, Tables 1, 2, 4, 5, and 6.

While ANSI/AAMI ST108 is a voluntary consensus standard, many accrediting bodies like The Joint Commission and CMS use these standards to assess compliance with best practices. Failure to align with ST108 can put patient safety, accreditation, and operational efficiency at risk.

ANSI/AAMI ST108 itself is a voluntary consensus standard. AAMI standards are not automatically mandatory simply because they exist. However, voluntary standards can become enforceable or expected when they are adopted by government agencies, procurement authorities, accrediting bodies, facility policy, contracts, or other regulatory mechanisms.

For healthcare facilities, the more practical question is not only whether ST108 is “mandatory” today, but whether the facility can demonstrate a defensible water management program that aligns with current standards, accreditation expectations, manufacturer instructions for use, and patient safety responsibilities. ST108 also notes that CMS and The Joint Commission have water management expectations related to oversight, implementation, water quality production, and risk assessment.

Source within ANSI/AAMI ST108:2023: AAMI Standard notice, Clauses 4.3, 5.1, 10.2, 11.2.

ANSI/AAMI ST108 does not provide a simple blanket “yes” or “no” answer for operating during an active boil water notice. The decision should be made through the facility’s water management program, risk assessment, and multidisciplinary team, based on whether the department can verify that water used for medical device processing meets the required quality for the intended use.

ST108 does provide specific steps for extended boil water alerts and actions after alerts are lifted. These include flushing and disinfecting water treatment equipment and loops, flushing the feedwater source, draining and disinfecting storage tanks, changing pretreatment filters, backwashing carbon tanks, regenerating softeners, cleaning and disinfecting RO membranes, disinfecting distribution loops, checking steam systems, replacing DI tanks when used, and replacing final loop filters. In short, SPD operations should not resume normal water-dependent processing until the facility has verified that the water system is safe and producing water that meets the appropriate specifications.

Source within ANSI/AAMI ST108:2023: Clauses 10.4, 13.2, 13.3, Tables 2, 5, and 6.

Poor water quality can affect medical devices, processing equipment, workflow, and patient safety. ANSI/AAMI ST108 identifies potential adverse effects to medical devices such as corrosion, pitting, scaling, biofilm buildup, increased microbial load, and increased endotoxin content. It also identifies process-related effects such as decreased cleaning agent performance and degradation of water systems or processing equipment through biofouling or scaling.

For patients, inadequate water quality can contribute to indirect risks such as infection, toxicity from residual chemicals, tissue irritation, pyrogenic reactions, device malfunction, ineffective cleaning or disinfection, and contamination of processed devices. For SPD teams, the operational impact may show up as instrument staining, corrosion, residue, rework, equipment problems, delayed trays, and uncertainty about whether devices were processed under acceptable conditions.

Source within ANSI/AAMI ST108:2023: Clauses 5.1, 5.2.1, 6.3, 7.2, Annex A.3, Annex B.1, Annex I.

ANSI/AAMI ST108 provides recommended minimum frequencies for routine water quality monitoring at both the water generation system and the point-of-water-use. For Utility Water, many parameters are recommended at least quarterly. For Critical Water, several chemical parameters are recommended monthly, conductivity at the generation system is recommended daily, and bacteria and endotoxin are recommended at least monthly. At the point-of-water-use, Critical Water testing for pH, conductivity, total alkalinity, total hardness, bacteria, and endotoxin is recommended at least monthly. Daily visual inspection of equipment interiors is also recommended for Utility Water, Critical Water, and steam-related equipment.

These are minimum recommendations. ST108 notes that testing frequency may need to increase if problems arise, if a risk assessment identifies higher-risk sampling points, or after events such as repairs, disinfection, supply interruptions, boil-water situations, construction, or restoration of supply.

Source within ANSI/AAMI ST108:2023: Clauses 9.1, 10.3.1, 10.4, Tables 4, 5, and 6.

There is no single equipment package that automatically satisfies ANSI/AAMI ST108. The equipment needed depends on incoming water quality, the volume and flow rate required, the points-of-use served, the water quality needed, and the specific processes being supported. ST108 explains that the first step in selecting water treatment equipment is to analyze incoming water to determine contaminants and their concentrations.

For Utility Water, typical treatment may include pretreatment equipment that removes larger particulates, reduces hardness, removes organics or chlorine as needed, and reduces dissolved solids. For Critical Water, systems generally require more extensive treatment and may include pretreatment, primary treatment such as RO and/or DI, storage, distribution, and final treatment to control microorganisms and endotoxin. ST108 also describes treatment technologies such as sediment filtration, softening, carbon adsorption, reverse osmosis, deionization, ultrafiltration, UV disinfection, ozone, hot water disinfection, and chemical disinfection.

Source within ANSI/AAMI ST108:2023: Clauses 8.1, 8.2, 8.3.1, 8.3.2.1, 8.3.2.2, Annex E, Table E.1, Annex F.

Tap water may be used only if it meets the appropriate water quality requirements for the intended use and is compatible with the device, equipment, and chemistry manufacturer’s written instructions for use. ANSI/AAMI ST108 defines tap water by where it comes from, not by its quality. The standard specifically notes that tap water may not meet the requirements for Utility Water.

For cleaning stages and certain washer-disinfector stages, Utility Water is generally the minimum acceptable quality. If tap water does not meet Utility Water specifications, it should be treated before use. For final rinsing of critical and semi-critical devices, Critical Water is generally required or recommended because final rinse water should not leave contaminants, microorganisms, endotoxin, or residues on devices. For sterilizers, the appropriate feedwater depends on the sterilizer design and manufacturer’s written IFU, and steam condensate should meet the relevant ST108 criteria.

Source within ANSI/AAMI ST108:2023: Clauses 3.85, 6.2, 7.3.1.2, 7.3.2.1, 7.3.2.3.5, 7.5.1, 8.1, Table 2, Annex D.3.

ANSI/AAMI ST108 addresses steam purity, meaning the chemical characteristics of steam when tested as condensate. The standard does not cover physical steam quality characteristics such as dryness, noncondensable gases, or superheat; those are addressed in ANSI/AAMI ST79. ST108 focuses on whether steam condensate meets defined water quality parameters that could affect sterilizer performance, medical devices, or sterilized loads.

Steam purity is affected by the quality of the feedwater used to generate steam and by the steam distribution system. ST108 notes that steam should be free from contaminants in concentrations that could impair the sterilization process, damage the sterilizer, or damage the devices being sterilized. Poor steam purity or distribution issues can contribute to staining, residues, corrosion, wet packs, inconsistent sterilizer performance, and other processing problems.

Source within ANSI/AAMI ST108:2023: Clauses 1.3, 3.76, 3.77, 6.2, 7.5.1, Table 2, Annex D.3.

Utility Water is water that may come from the tap but may require treatment to meet the ST108 quality values. It is mainly used for flushing, washing, and intermediate rinsing. Critical Water is a higher-purity category of water that meets the more stringent requirements in ST108 Table 2 and generally requires a multi-step treatment process.

The biggest practical difference is where each water type is used. Utility Water is predominantly used during earlier processing steps. Critical Water is mainly used for the final rinse after high-level disinfection, the final rinse for critical devices before sterilization, and as feedwater for process steam production. ST108 also cautions that using Critical Water for every processing step can be unnecessary, costly, and potentially damaging to certain water systems or processing equipment.

Source within ANSI/AAMI ST108:2023: Clauses 3.21, 3.90, 6.2, Table 2, Annex A.1, Annex A.2, Annex D.

ANSI/AAMI ST108 makes water quality a shared responsibility. The standard identifies a multidisciplinary team responsible for the water management program and for maintaining an acceptable level of water quality. Senior organizational leadership should select the individual or individuals responsible for leading the team.

Facilities Engineering personnel are responsible for water system installation, qualification, validation for the appropriate water quality, and water system maintenance. Medical device processing personnel are responsible for cleaning, disinfection, inspection, and sterilization of medical devices and should understand the water quality monitoring performed in processing areas. Infection Prevention participates in policy development, risk assessment, review of water monitoring results, and corrective action planning. Water treatment specialists are involved in the selection, integration, qualification, and validation of water treatment equipment. All members of the multidisciplinary team manage the water management program.

Source within ANSI/AAMI ST108:2023: Clauses 4.1, 4.2, 4.3, 4.3.2, 4.3.3, 4.3.4, 4.3.7, 4.4, Table 1.

One common mistake is assuming that a single piece of equipment, such as an RO system, automatically equals ST108 compliance. ST108 is broader than equipment; it includes water quality selection, treatment system design, qualification, routine monitoring, maintenance, documentation, risk analysis, and continuous quality improvement.

Another mistake is assuming tap water is acceptable without verifying that it meets Utility Water requirements. ST108 states that tap water refers to the source location, not the water quality, and that tap water may require treatment to meet Utility Water or Critical Water specifications. Other common mistakes include failing to form a multidisciplinary water management team, not testing at the point-of-use, overlooking final rinse requirements, not trending results, failing to define alert and action levels, not responding properly to out-of-range results, neglecting routine maintenance, and overlooking special situations such as construction, shutdowns, repairs, disinfection, or boil-water events.

Source within ANSI/AAMI ST108:2023: Clauses 3.85, 4, 5.1, 6.2, 8.1, 8.3.2.2, 8.4.1, 9.1, 10.2, 10.4, 11.2, 12, 13, Tables 1, 2, 4, 5, and 6.

No. Having a reverse osmosis (RO) system may be an important part of producing water that supports ANSI/AAMI ST108 compliance, but an RO system alone does not make a facility compliant. ST108 focuses on the quality of water delivered to the point-of-use and used during medical device processing, including cleaning, rinsing, disinfection, and sterilization. Compliance depends on whether the correct water quality is selected for each processing step, whether that water meets the required specifications, and whether the system is properly qualified, monitored, maintained, and documented over time.

ST108 identifies Critical Water as water that generally requires a multi-step treatment process, which may include pretreatment, RO and/or DI, storage, distribution, and final treatment to help remove microorganisms, inorganic material, and organic material. In other words, RO may be part of the solution, but the facility still needs a complete water management program, defined team responsibilities, routine testing, trending, maintenance, and corrective action procedures.

Source within ANSI/AAMI ST108:2023: Clauses 1.2, 4, 6.2, 8.3.2.2, 9, 10, and Table 2.

Water quality testing is only one part of an ANSI/AAMI ST108 program. Testing helps verify whether water meets defined quality characteristics, such as pH, conductivity, hardness, bacteria, endotoxin, color, and turbidity. However, ST108 also addresses broader program elements, including water quality selection, water treatment system design, installation qualification, operational qualification, performance qualification, routine monitoring, maintenance, documentation, and continuous quality improvement.

A facility can perform water testing and still have gaps in its overall ST108 program if it has not defined responsibilities, established alert and action levels, documented monitoring procedures, developed corrective action processes, or verified that the correct type of water is used at each stage of medical device processing. A strong ST108 approach connects testing data to operational decisions.

Source within ANSI/AAMI ST108:2023: Clauses 1.2, 4, 8.4.1, 9, 10, 11, Tables 2, 4, 5, and 6.

ANSI/AAMI ST108 defines an alert level as a monitoring value that provides early warning of a deviation from specified conditions. An action level is a monitoring value that requires immediate intervention. In practical terms, an alert level tells the team that water quality may be trending in the wrong direction, while an action level means the facility needs to respond right away.

ST108 explains that ongoing monitoring can be used to establish baseline data and identify trends before water quality fails to meet the required specification. When results move outside the facility’s alert limits, the excursion should prompt investigation into possible causes and risks. When results exceed action levels, the water quality values are not to be exceeded, and immediate intervention is needed.

Source within ANSI/AAMI ST108:2023: Clauses 3.3, 3.4, 8.4.1, 10.3.1, Table 4, and Annex G.1.2.

If water quality results are out of range, the facility should follow its water management plan and involve the appropriate members of the multidisciplinary water management team. The response should include reviewing the affected water quality parameter, determining whether the water is still suitable for the intended processing step, assessing potential risk to devices and patients, documenting the event, investigating the cause, taking corrective action, and retesting as appropriate.

ST108 emphasizes that water quality monitoring is intended to confirm that control strategies are working as expected and to detect when remedial action may be needed. For example, if bacteria or endotoxin levels exceed acceptable limits for Critical Water, that water should not be used for final rinsing of critical devices until the issue is corrected and an acceptable source of water is available. The standard also notes that excursions outside alert levels should prompt investigation to identify assignable causes and associated risks.

Source within ANSI/AAMI ST108:2023: Clauses 5.1, 10.2, 10.3.1, 10.4, 11.2, Annex H.6, and Tables 2, 4, 5, and 6.

ANSI/AAMI ST108 recommends a multidisciplinary team because water quality affects more than one department. The team may include senior organizational leadership, Facilities Engineering, Infection Prevention, Sterile Processing or other medical device processing personnel, Clinical Engineering, surgical suite or procedure area personnel, and a water treatment specialist.

This team is responsible for developing, implementing, and documenting the applicable requirements of the water management program. Facilities personnel typically support water system installation, qualification, validation, and maintenance. Medical device processing personnel help ensure that the proper water quality is available and used for the various stages of processing. Infection Prevention participates in policy development, review of monitoring results, risk assessment, and corrective action planning.

Source within ANSI/AAMI ST108:2023: Clauses 4.1, 4.2, 4.3, 4.3.2, 4.3.3, 4.3.4, 4.3.7, and Table 1.

ANSI/AAMI ST108 provides recommended minimum monitoring frequencies for Critical Water at both the water generation system and the point-of-water-use. At the water generation system, conductivity is recommended for daily monitoring, while pH, total alkalinity, total hardness, bacteria, and endotoxin are recommended at least monthly. At the point-of-water-use, pH, conductivity, total alkalinity, total hardness, bacteria, and endotoxin are recommended at least monthly, with daily visual inspection of equipment interiors for residue, staining, scaling, or discoloration.

These are minimum recommended frequencies. ST108 notes that testing may need to be increased if problems arise, if the risk assessment identifies higher-risk sampling points, or if conditions such as construction, supply interruption, system repair, disinfection, boil-water situations, or restoration of supply occur.

Source within ANSI/AAMI ST108:2023: Clauses 9.1, 10.4, Tables 5 and 6.

Utility Water is generally used for flushing, washing, and intermediate rinsing during medical device processing. ANSI/AAMI ST108 describes Utility Water as water that may come from the tap but may require treatment at the facility to meet the required quality values. Tap water should not automatically be assumed to meet Utility Water requirements.

Utility Water may be appropriate for point-of-use treatment, manual cleaning, washer stages, post-wash rinsing, and certain disinfection processes, depending on the device, equipment, chemistry, and manufacturer’s instructions for use. However, facilities should verify that the water is compatible with cleaning agents, medical devices, and processing equipment, and that it meets the relevant ST108 values for Utility Water.

Source within ANSI/AAMI ST108:2023: Clauses 3.85, 3.90, 6.2, 7.3.1.1, 7.3.1.2, 7.3.1.3, 7.3.2.3, Table 2, and Annex A.1.

Critical Water is used in higher-risk processing steps where water quality can directly affect the final condition of a medical device. ANSI/AAMI ST108 describes Critical Water as water that meets the quality requirements in Table 2 and is mainly used for the final rinse after high-level disinfection, the final rinse for critical devices before sterilization, and as feedwater for process steam production.

Critical Water is important because final rinse water should not add microorganisms, endotoxin, inorganic residue, or organic contaminants back onto devices after cleaning or disinfection. ST108 notes that Critical Water generally requires extensive treatment through a multi-step process and includes defined limits for bacteria, endotoxin, conductivity, total organic carbon, hardness, and other contaminants.

Source within ANSI/AAMI ST108:2023: Clauses 3.21, 6.2, 7.1, 7.3.1.4, 7.3.2.3.5, 7.4.2, 7.5.1, Table 2, and Annex A.2.

ANSI/AAMI ST108 affects sterile processing workflow because water quality is a consideration at multiple stages of medical device processing, including point-of-use treatment, cleaning, rinsing, disinfection, final rinsing, and sterilization-related processes. The standard makes clear that the correct type of water should be selected based on the device, the processing step, and the method of disinfection or sterilization.

In daily practice, this means SPD teams need to know which water quality is required for each step, recognize signs of possible water quality issues, participate in monitoring activities where appropriate, and escalate concerns when instruments, equipment chambers, or processed devices show residue, staining, scaling, discoloration, or corrosion. ST108 also emphasizes that medical device processing personnel should receive education, training, and competency verification related to water quality and the risks of improper water system characteristics.

Source within ANSI/AAMI ST108:2023: Introduction, Clauses 4.3.4, 5.1, 7.2, Figure 1, Table B.1, and Annex I.

ANSI/AAMI ST108 makes Facilities and Engineering central to medical device processing water quality. Facilities Engineering personnel are identified as responsible for water system installation, qualification, validation for the appropriate water quality, and system maintenance. The standard also places Facilities in a key role for water quality assessment, routine sampling, implementation of water treatment processes, and determining appropriate methods or equipment for the facility’s water supply.

Because water quality can vary based on source water, building plumbing, treatment equipment, distribution loops, storage tanks, maintenance practices, repairs, construction, shutdowns, and supply interruptions, ST108 requires close collaboration between the teams that process medical devices and the teams that establish and maintain the water treatment system. Facilities and Engineering teams are not just supporting players; they are part of the compliance and patient safety infrastructure.

Source within ANSI/AAMI ST108:2023: Introduction, Clauses 4.3, 4.3.2, 4.4, 8.3, 8.4.1, 9.1, 10.1, 12, 13, and Table 1.