Author
Will Fitzgerald, Water Safety Business Manager
Why AAMI ST108 Matters in Healthcare?
In hospitals and healthcare facilities, water quality is foundational to patient safety. Every surgical instrument, endoscope, and reprocessed device must be cleaned and sterilized using water that meets strict purity standards. Recognizing this, the Association for the Advancement of Medical Instrumentation (AAMI) developed ST108, a standard that establishes specific quality requirements for water used in medical device processing.
AAMI ST108 provides detailed guidance on when and where to use each water quality type, how to maintain it, and how to verify compliance through testing and monitoring. For hospitals, ambulatory surgery centers, and other healthcare environments, adherence to AAMI ST108 ensures that water systems meet the standards necessary for sterile processing and infection prevention.
Design & System Requirements for Hospital Water Systems
AAMI ST108 emphasizes a well-designed and continuously monitored water system, crucial for hospital central sterile departments (CSDs) and other reprocessing areas. Key Recommendations Include:
System Design
- Hospitals should implement a continuous loop system with essential components such as carbon filtration or chlorine destruct chemicals, softeners, reverse osmosis (RO), deionization (DI), an RO tank with conical bottom, a circulating pump, optional UV disinfection, and a 0.2-micron bacteria filter.
- The loop should maintain a return velocity of 3–5 feet per second (FPS) to minimize microbial growth.
Materials & Isolation
- Critical water loops should use Schedule 80 PVC, polypropylene, or high-density polyethylene piping.
- Hospital water systems should be dedicated solely to medical device reprocessing — not shared with dialysis or laboratory water systems.
Monitoring & Alerts
- Continuous monitoring and alarm systems should alert staff when conductivity deviates from limits or when filters and membranes require replacement.
- Reverse osmosis units should have a “divert-to-drain” safety feature for poor-quality water.
Figure 1: The flow diagram illustrates water system layout and recommended monitoring points
Disinfection & Preventive Maintenance in Hospitals
To prevent biofilm formation and bacterial contamination, AAMI ST108 recommends monthly disinfection of the entire water loop and RO tank. Hospitals can use agents such as:
- Ozone
- Chlorine or sodium hypochlorite
- Hydrogen peroxide
- Peracetic acid
These steps are critical in hospital sterile processing departments to ensure consistent water purity and avoid contamination of surgical instruments.
Testing, Monitoring & Frequency for Healthcare Facilities
ST108 defines rigorous testing schedules and quality limits for various contaminants, ensuring hospital compliance with infection control and accreditation standards.
Routine Testing in Healthcare Settings
- Daily: Conductivity monitoring (preferably through automated sensors)
- Monthly: Heterotrophic Plate Count (HPC) and Endotoxin testing at loop entry and return
- Quarterly: pH, hardness, and alkalinity assessments
- Annually: Ionic contaminant analysis
Critical Water Quality Standards
From the AAMI ST108 table on page 2, hospital and healthcare water systems should maintain:
- Bacteria: < 10 CFU/mL
- Endotoxin: < 10 EU/mL
- Conductivity: < 10 µS/cm
- Total Organic Carbon: < 1 ppm
- Total Hardness: < 1 ppm
Figure 2: Apex ST108 Water Quality
These benchmarks support compliance with infection prevention, sterile processing guidelines, and hospital accreditation requirements.
Water Categories in Hospital Environments
- Utility Water: For general cleaning, flushing, and initial rinsing
- Critical Water: For final rinsing and steam generation
- Steam: Used in sterilizers and autoclaves
Hospitals must ensure each category maintains proper isolation and is used for its intended purpose to prevent cross-contamination between processing stages.
Apex: Supporting Hospital and Healthcare Compliance
Apex delivers end-to-end water and process solutions for hospitals and healthcare systems. Our team helps healthcare facilities:
- Design and install AAMI ST108-compliant systems
- Implement automated data collection and water quality tracking
- Perform routine disinfection, validation, and documentation
- Ensure full compliance with AAMI, ASHRAE, and hospital accreditation standards
At Apex, we partner with hospitals to provide more than equipment — we deliver reliability, traceability, and assurance that your water systems are compliant with current industry standards.
Contact Apex
To learn more about AAMI ST108 compliance or schedule a system evaluation, contact your Apex representative or email info@teamapex.com.
Will Fitzgerald
Water Safety Manager, Apex Water and Process
Will has 13 years of experience in water management and risk mitigation pertaining to Legionella and other waterborne pathogens. He is also certified in ASSE 12080 Legionella Water Safety and Management.