How Can Healthcare Facilities Meet AAMI ST108A Water Quality Requirements?

Healthcare facilities meet AAMI ST108 water quality requirements through reverse osmosis systems, electrodeionization, and UV sterilization that reduce total dissolved solids to ≤10 mg/L and bacterial counts to ≤10 CFU/100mL for critical water used in medical device reprocessing. AAMI ST108:2023 published in August 2023 establishes microbiological, chemical, and physical parameters for water used in healthcare device processing. Compliance addresses 1.7 million annual healthcare-associated infections linked to contaminated medical instruments. Hospitals, ambulatory surgery centers, and dialysis facilities require compliant water treatment systems for sterile processing departments. This guide provides technical requirements and implementation approaches for AAMI ST108 compliance.

What Are AAMI ST108 Water Quality Parameters?

AAMI ST108:2023 defines two water quality categories with specific microbiological, chemical, and physical limits for medical device reprocessing.

What Standards Apply to Critical Water?

Critical water for high-risk device processing requires ≤10 CFU/100mL bacterial count, ≤0.5 mg/L total hardness, and ≤10 mg/L total dissolved solids. Critical water parameters ensure surgical instrument sterility for immunocompromised patients and invasive procedures.

Critical Water Quality Parameters

What Standards Apply to Utility Water?

Utility water for general device cleaning requires ≤200 CFU/100mL bacterial count and ≤50 mg/L total dissolved solids. Healthcare facilities use utility water for washer-disinfectors, ultrasonic cleaners, and automated endoscope reprocessors in sterile processing departments. Utility water standards exceed municipal tap water quality but allow higher contaminant levels than critical water.

Which Water Treatment Systems Achieve AAMI ST108 Compliance?

Healthcare facilities achieve AAMI ST108 compliance through three primary technologies: reverse osmosis systems reducing TDS to <10 mg/L, electrodeionization providing continuous deionization, and UV sterilization operating at 254-nanometer wavelength.

How Do Reverse Osmosis Systems Meet AAMI ST108?

Reverse osmosis systems achieve 98.5-99% TDS rejection through semi-permeable membranes operating at 80-200 psi pressure. Commercial RO systems ranging from 2,000 to 190,000 gallons per day (gpd) serve facilities with 50-500+ bed capacity. RO membranes reduce bacterial counts to non-detect levels and total hardness from 87 mg/L to <0.5 mg/L.

A 300-bed hospital requires 36,000 gpd RO capacity based on 120 gallons per bed daily consumption for sterile processing operations. Ultra-low-energy membranes consume 20% less energy than standard RO elements while maintaining 99% rejection rates.

What Role Does EDI Play in Water Purification?

Electrodeionization (EDI) systems provide continuous deionization without chemical regeneration, reducing TDS to <0.1 mg/L through ion-exchange membranes and electrical current. EDI eliminates acid-base regeneration chemical costs compared to conventional deionization systems. Healthcare facilities install EDI as post-treatment following reverse osmosis to achieve ultrapure water specifications. Automated sanitization cycles reduce maintenance labor versus manual regeneration systems.

How Does UV Sterilization Ensure Microbiological Compliance?

UV sterilization systems operating at 254-nanometer wavelength disrupt bacterial DNA without chemical additives. Healthcare facilities install UV systems as final treatment stage before point-of-use to maintain ≤10 CFU/100mL bacterial counts. UV systems meet AAMI ST108 disinfection requirements when sized for appropriate contact time and intensity measured in mW·s/cm². Systems are designed to meet AAMI ST108 microbiological parameters through validated UV dosage protocols.

What Steps Achieve AAMI ST108 Compliance?

Healthcare facilities achieve AAMI ST108 compliance through five sequential steps: water quality assessment, technology selection, system sizing, installation, and ongoing monitoring.

1. Conduct baseline water quality testing Test municipal feed water for TDS, hardness, bacterial count, chlorine, and pH levels. Identify gap analysis between current quality and AAMI ST108 parameters. Sterile processing departments measure daily water consumption in gallons to determine system capacity requirements.
2. Select appropriate treatment technologies Choose reverse osmosis for TDS reduction from typical 300-500 mg/L municipal water to <10 mg/L. Add EDI post-treatment for critical water applications requiring <0.1 mg/L TDS. Install UV sterilization as final barrier for microbiological control.
3. Calculate system sizing requirements Determine peak demand based on washer-disinfector cycles, autoclave operations, and instrument processing volume. Size systems for 120-150 gallons per bed per day in acute care hospitals. Include 25-30% capacity buffer for growth and maintenance downtime.
4. Install with proper distribution infrastructure Use stainless steel piping to prevent biofilm colonization in distribution loops. Install 0.2-micron point-of-use filters for final bacterial removal. Configure recirculation loops maintaining water temperature 60-80°F to inhibit Legionella growth.
5. Establish monitoring and documentation protocols Test critical water monthly for bacterial count, TDS, and hardness per AAMI ST108 requirements. Document test results, system maintenance, and membrane replacement for regulatory audits. Implement corrective action procedures when parameters exceed AAMI ST108 limits.

How Do Facilities Verify AAMI ST108 Compliance?

Facilities verify AAMI ST108 compliance through monthly water quality testing measuring bacterial count, TDS, hardness, and pH against published limits. Sterile processing departments collect samples at point-of-use locations including washer-disinfectors and final rinse stations. Laboratory analysis using heterotrophic plate count methods quantifies bacterial levels in CFU/100mL. Facilities document 12 consecutive months of compliance before Joint Commission surveys. Non-conforming results trigger immediate investigation, corrective action, and retesting within 48 hours.

Partner with Proven Water Treatment Expertise

AXEON Water Technologies engineers water purification systems for healthcare facilities requiring AAMI ST108 compliance. With 35 years of experience and 250,000+ commercial systems installed, AXEON provides reverse osmosis, electrodeionization, and UV sterilization solutions assembled in the United States. Contact AXEON's application engineering team at 1-800-320-4074 for system design consultation, water quality analysis, and technical support tailored to your facility's sterile processing requirements.