What Is the AAMI ST108A Standard and How Does It Affect Healthcare Water Systems?

AAMI ST108 replaces TIR34 as the mandatory water quality standard for medical device processing in healthcare facilities. AAMI ST108 is an ANSI-approved standard that establishes testing requirements for three water categories—utility, critical, and steam—used in sterile processing departments. Published in August 2023, ST108 impacts hospitals, ambulatory surgery centers, and healthcare facilities using water for instrument reprocessing. This article explains ST108 requirements, testing parameters, affected water treatment systems, and implementation considerations for healthcare facility compliance.

What Is the AAMI ST108 Standard?

AAMI ST108 is a mandatory water quality standard published by the Association for the Advancement of Medical Instrumentation (AAMI) that establishes testing requirements for water used in medical device processing. The full designation is ANSI/AAMI ST108:2023, approved August 4, 2023 by the American National Standards Institute (ANSI).

AAMI develops standards for medical devices and healthcare technology. ST108 replaces the previous TIR34 Technical Information Report, transitioning from voluntary guidance to a mandatory standard with enforceable requirements.

The standard applies to water used in reprocessing reusable medical devices including endoscopes, surgical instruments, and equipment processed through autoclaves and automated endoscope reprocessors. ST108 is expected to be referenced by Joint Commission standard EC.02.05.02 and CMS memorandum QSO-17-30 updates for regulatory enforcement.

What Are the Key Requirements of AAMI ST108?

AAMI ST108 requires healthcare facilities to test water across 18 parameters covering microbiological, chemical, and physical properties for three distinct water categories.

Water Categories Defined by ST108

ST108 establishes three water categories with specific quality requirements:

1. Utility Water: Initial source water entering the facility with minimal treatment, used for non-critical applications including equipment cooling and general cleaning operations
2. Critical Water: Extensively treated water meeting strict purity limits below 5 µS/cm conductivity, used for final rinse of medical devices and instrument processing in sterile processing departments
3. Steam: Water converted to steam for sterilization in autoclaves and local steam generators requiring specific chemical purity standards

Testing Parameters and Frequency

ST108 specifies approximately 18 testing parameters with defined limits and testing frequencies for critical water quality.

Testing frequency varies based on water category, with critical water requiring more frequent monitoring than utility water. Facilities must document all testing results and maintain records for regulatory inspections.

How Does ST108 Affect Healthcare Water Systems?

ST108 affects healthcare water systems by requiring extensive water treatment, continuous monitoring equipment, and multidisciplinary team coordination to meet mandatory quality standards.

Water Treatment System Requirements

Healthcare facilities use five primary treatment technologies to achieve ST108 compliance:

• Reverse osmosis systems achieve 98.5-99% TDS rejection to produce critical water meeting conductivity limits below 5 µS/cm
• Deionization systems remove dissolved minerals including calcium, magnesium, iron, and copper to prevent scaling and contamination
• Ultraviolet sterilization systems control microbiological parameters without chemical additives for endotoxin reduction
• Sediment and carbon filtration systems remove particulates and chlorine during pretreatment stages
• Electrodeionization systems produce ultrapure water exceeding 2 MΩ·cm resistivity for final rinse applications requiring highest purity

Facility Implementation Considerations

Existing water systems installed under TIR34 guidance may require retrofitting or replacement to meet stricter ST108 conductivity and endotoxin limits. Facilities need water testing capabilities through third-party laboratories certified for AAMI ST108 compliance or in-house testing equipment. ST108 requires coordination between sterile processing departments, facilities engineering, infection prevention, and quality assurance teams for water management program oversight. Regulatory compliance demands accurate record-keeping of daily testing results, maintenance logs, and corrective action responses for accreditation inspections. Capital expenditures for water treatment equipment, ongoing testing costs, and staff training represent significant financial considerations for facility planning.

What Are the Differences Between TIR34 and ST108?

TIR34 was a voluntary Technical Information Report providing guidance, while ST108 is a mandatory ANSI-approved standard with enforceable requirements and stricter testing parameters.

The transition from TIR34 to ST108 introduces four major changes affecting healthcare facility compliance.

Facilities operating under TIR34 protocols must assess their current water systems against ST108 requirements to identify compliance gaps. The mandatory nature of ST108 increases regulatory enforcement risk through Joint Commission and CMS inspections.

Who Needs to Comply with AAMI ST108?

Healthcare facilities that reprocess reusable medical devices using water-based cleaning or sterilization processes must comply with AAMI ST108 standards.

ST108 applies to seven facility types:

• Acute care hospitals with sterile processing departments (SPD) handling surgical instruments
• Ambulatory surgery centers performing outpatient procedures requiring instrument reprocessing
• Endoscopy centers using automated endoscope reprocessors (AERs) for scope cleaning
• Dialysis facilities requiring ultrapure water for patient treatment and equipment processing
• Dental clinics sterilizing reusable dental instruments with water-based systems
• Veterinary hospitals with surgical capabilities and instrument sterilization needs
• Research laboratories processing reusable medical equipment

Any facility using water for final rinse steps in medical device reprocessing falls under ST108 scope regardless of facility size or patient volume.

What Are the Benefits of ST108 Compliance?

ST108 compliance delivers five primary benefits including improved patient safety, regulatory readiness, equipment longevity, infection control, and standardized quality assurance.

1. Patient Safety Enhancement: Reduces healthcare-associated infections (HAIs) by ensuring water quality eliminates contamination risks during instrument reprocessing
2. Regulatory Compliance: Meets Joint Commission, CMS, and state health department requirements preventing accreditation failures and regulatory citations
3. Equipment Protection: Prevents scale buildup, corrosion, and premature failure of sterilization equipment including autoclaves and endoscope reprocessors
4. Infection Control: Supports facility-wide infection prevention programs by controlling waterborne pathogen exposure risks
5. Quality Standardization: Establishes consistent water quality across departments and shifts through documented testing protocols

Conclusion

AAMI ST108 establishes mandatory water quality requirements for healthcare facilities reprocessing medical devices with three defined water categories and 18 testing parameters. Healthcare water systems require treatment technologies including reverse osmosis, deionization, and UV sterilization to meet conductivity limits below 5 µS/cm and microbiological standards under 10 CFU/mL. Facilities must implement testing programs, upgrade existing systems, and coordinate multidisciplinary teams for compliance.

AXEON Water Technologies offers ultrapure water systems including RDP-Series, X1S-Series, and EDI-Series designed to support healthcare facility compliance with ST108 requirements. Healthcare facilities should assess current water systems against ST108 requirements to identify necessary upgrades before regulatory enforcement intensifies through Joint Commission and CMS inspections.