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What is ANSI/AAMI ST108?

The Association for the Advancement of Medical Instrumentation (AAMI) has developed and published a new standard, ANSI/AAMI ST108:2023 – Water for the Processing of Medical Devices. This new standard replaces AAMI TIR34:2014. ANSI/AAMI ST108:2023 is the new industry consensus standard for selecting the water quality, testing, and monitoring necessary for the reprocessing of medical devices and surgical instruments. Key differences and updates from TIR34 include:

  1. Requirement for the facility to establish a multi-disciplinary team responsible for water quality and the water management program.
  2. Expansion of water quality types to include steam.
  3. Establishment of expanded water quality criteria for system performance qualification.
  4.  Routine water quality monitoring requirements at both the water generation system and at departmental points-of-use.

Adverse Effects of Poor Water Quality

Water impurities can have adverse effects to medical device processing, including:

  1. Adverse effects to the Product:
       • Corrosion, pitting, scaling.
       • Biomass build-up.
       • Increase microbial load or endotoxin content.
    2. Adverse effects to the Process:
       • Decreased effectiveness of detergents.
       • Degradation of the water system (biofouling or scaling).
    3. Adverse effect to the Patient:
       • Infection
       • Toxicity

It is important that sterile processing personnel understand the water quality issues that can contribute to adverse patient events and be aware of some of the gross indicators that suggest that there may be problems with the water quality.

Categories of Water Quality for Medical Device Processing

AAMI ST108 defines three categories of water quality for medical device processing:


  1. UTILITY WATER – water that comes from the tap that may require further treatment. Used for flushing, washing, and rinsing of medical devices.
  2. CRITICAL WATER – water that is extensively treated to ensure microorganisms, inorganic and organic materials are removed. Used for final rinse or steam generation.
  3. STEAM – water that is heated via a boiler or steam generator until it changes from liquid phase to vapor phase. Steam can be fed from a central location within the hospital such as a boiler plant or created via a steam generator within a sterilizer. Used for sterilization of medical devices.

What testing is required by AAMI ST108?

ST108 requires extensive testing. “Utility water” used for washing devices, steam condensate used for sterilization, and “critical water” used for reprocessing, sterilizing, and rinsing must be tested for a total of about 18 parameters including: 

  • Microbial parameters (e.g., heterotrophic bacteria; endotoxins)
  • Chemical parameters (e.g., dissolved minerals; metals)
  • General water quality parameters (e.g., pH, TOC, turbidity, conductivity, total organic carbon)

How Should Sterile Processing Departments and Facilities Implement AAMI ST108?

 There are four steps sterile processing departments and hospital facilities teams should take to achieve critical water quality:

1) Water Quality Assessment
Tap water from a public utility source should be analyzed by an accredited facility with expertise in water quality to determine whether the water requires treatment and, if so, what type of treatment.

2) Implementation of Water Treatment Plan
If treatment is required, personnel should ensure that treatment processes are implemented to provide the type of water quality needed for the medical device processing needs of the facility.

3) Assurance of Proper Water Quality
Process water used in medical device reprocessing areas should be audited to determine whether water of the correct quality is being used for the devices being reprocessed in each area. If not, the water treatment should be modified as necessary.

4) Ongoing Water Monitoring
Where applicable, routine and ongoing monitoring procedures should be established to ensure that the treated water is of adequate quality for medical device reprocessing. Water maintenance personnel and device reprocessing personnel should communicate effectively to ensure that action is taken when inadequate water quality is detected.

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Meras Water Solutions has over 20 years of experience supporting and designing water quality programs

If you have any questions about this new standard or other water quality topics, please contact:

Jaime Leal at  209-900-4534 or [email protected].