AAMI ST108 & Critical Water for Autoclaves: What ASCs Need to Know

A major step forward in patient safety, ANSI/AAMI ST108 establishes new minimum water quality requirements for water used in the cleaning, rinsing, disinfection, and sterilization of reusable medical devices. Despite providing guidance on water quality management for sterile processing, ST108 has also created confusion, especially regarding test protocols, water treatment, and critical water requirements.

In this article, we’ll dispel common misconceptions pertaining to ST108 and tell facilities managers what they really need to know about this standard.

What Is AAMI ST108?

AAMI ST108 is a new standard that replaces the previous technical information report, AAMI TIR34. Unlike TIR34, ST108 is a formal, enforceable standard now being adopted or referenced by regulatory and accreditation bodies in healthcare. The AAMI working group is currently developing AAMI TIR119, Guidance on Healthcare Implementation and Use of ANSI/AAMI ST108. We’ll update this blog post as AAMI releases its latest recommendations.

AAMI ST108 Categories of Water & Steam

ST108 defines three categories of water for sterile processing: utility water, critical water, and steam.

ST108 Water Categories for Sterile Processing

For each category of water, ST108 defines a specific set of water quality characteristics that healthcare facilities must test through the year to guarantee compliance.

ST108 Routine Water Quality Monitoring Requirements*

* Performance testing requirements per ST108 include a more extensive list of water characteristics, including trace metal elements. Performance testing is required during the installation and qualification of a new water treatment system and during periodic system performance reviews.

How to Avoid Costly Testing Kits

The extensive testing requirements outlined by ST108 can be intimidating for facilities managers. A key point that’s often overlooked with ST108 as it pertains to steam sterilizers is that facilities only need to test the steam being fed into the autoclave chamber. The saving grace is that routine (quarterly) steam testing under ST108 requires only the seven parameters listed above.

While endotoxins can exist in water used to generate steam, studies have shown that devices exposed to the steam possess insignificant endotoxin levels. This is an important note, as bacteria and endotoxin tests from water testing laboratories can add $300 or more to the cost of a routine water quality test.

Do Healthcare Facilities Need to Use Critical Water for Steam Generation?

There’s a common misconception that all water used in the reprocessing cycle — including water used for steam generation in autoclaves — must now meet ST108’s critical water requirements. This has, naturally, raised concerns for facilities managers, who must now worry about the cost and complexity of retrofitting their existing infrastructure with costly and advanced water treatment systems to meet this perceived requirement.

Critical water systems require additional post-treatment beyond typical reverse osmosis (RO) or deionization (DI) filtration systems. Commonly marketed critical water systems include ultraviolet (UV) disinfection, bacteria and endotoxin filtration, and a continuous recirculation loop to prevent recontamination and comply with ST108’s bacteria, endotoxin, and total organic carbon (TOC) limits. These added components significantly increase the overall cost of a water treatment system.

But there’s good news: ST108’s critical water requirements apply specifically to the final rinse after high-level disinfection — that is, the final rinse stage in washers before steam sterilization. While healthcare facilities are free to use critical water to generate steam if they so choose (or if required by medical device instructions for use), they’re also fine to use simpler water treatment systems, provided that the water quality meets steam condensate testing criteria within ST108 and sterilizer manufacturer requirements.

This clarification is crucial, as it can help healthcare facilities avoid unnecessary capital expenditures and equipment downtime while still fully complying with current standards.

The Role of Water Quality & Sterilizer Construction for ST108 Compliance

Although critical water systems aren’t required to meet ST108, Consolidated Sterilizer Systems recommends using autoclaves with a fully stainless steel construction — including process piping and steam generator fed with DI water — for consistent compliance.

ST108 does not explicitly prohibit the use of house steam or carbon steel steam generators for sterilization in healthcare facilities. However, Consolidated has found that using “dirty steam” increases the risk of failing to meet the testing criteria outlined for steam condensate in ST108.

Ultimately, it’s the responsibility of each healthcare facility to determine its acceptable risk based on budget, but Consolidated’s internal studies concluded that stainless steel steam generators are best practice for ST108 compliance. Inherent iron and copper levels in steel steam generators and brass, bronze, copper, or cast-iron steam piping can lead to deposits on instruments, stain or corrode equipment, and compromise patient safety.

The Role of Water Quality in Autoclave Performance

Beyond ST108, water quality plays a critical role in autoclave performance and longevity. Water used for generation can contribute to equipment degradation if it contains high levels of minerals, chlorine, or other contaminants. These impurities can lead to sediment buildup and corrosion and reduce the efficiency of the steam piping system, the steam generator, and the autoclave itself, potentially resulting in costly maintenance or premature equipment failure.

While ST108 focuses on steam condensate quality, steam generator feedwater quality is critical for autoclave longevity and performance. Healthcare facilities should use house steam or carbon steel generators with tap or RO water within Consolidated requirements. Most carbon steel generators rely on water conductivity for level control, meaning the water cannot be too pure. Stainless steel generators operate on float-based controls and require DI feedwater.

The images above illustrate the stark contrast between a stainless steel and a carbon steel generator after only a few months of operation. While the image of the carbon steel generator is exaggerated due to a lack of maintenance, it still demonstrates why stainless steel is preferred for ST108, where any steam contamination can compromise compliance.

By using high-quality water for your autoclave, you can prevent long-term damage to equipment, reducing both maintenance costs and the risk of operational downtime — an imperative for high-volume healthcare facilities.

How Healthcare Facilities Should Move Forward to Comply with ST108

First and foremost, the primary purpose of ST108 is to minimize the risk of patient infection by ensuring surgical instruments and medical devices are thoroughly cleaned, disinfected, and sterilized before each use. Maintaining water quality is essential to reducing risk to patients because it prevents the transfer of microorganisms from feedwater into utility water, critical water, and steam. Water quality and preventative maintenance are also vital to the operational performance of any healthcare facility, as proper upkeep ensures the durability, reliability, and longevity of sterilization equipment.

Regular water quality testing is imperative to comply with ST108. As outlined by AAMI, steam condensate should be tested at least quarterly; Consolidated recommends testing on-board generators or facility boiler feedwater at least annually. Facility multidisciplinary teams should work together to assess water quality, implement appropriate water treatment solutions, and ensure ongoing maintenance and compliance.

It will take time to bring the thousands of surgery centers and hospitals around the country into compliance with ST108. But with proper maintenance and engineering controls, facility managers will find that house steam or steel generator steam systems can comply with ST108. However, should existing systems show signs of degradation or fail to meet this new standard’s requirements, an upgrade may be necessary. Though costly, transitioning to a stainless steel generator is the optimal long-term solution to enhance patient safety and reduce operational risk.

Consolidated is here to help healthcare facilities comply with AAMI ST108 specifications while avoiding costly overhauls whenever possible. From our line of healthcare sterilizers to our water quality testing kits, we have the equipment and expertise to meet the demands of even the highest volume facilities.

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