Water systems in sterile processing departments (CPD, Central Sterile, or SPD) across the United States are undergoing significant changes due to the new AAMI standard released in 2023: AAMI ST108. This article explores the evolving landscape of water systems for sterile processing and the new recommendations from ST108.

Historical Context

Historically, water systems for central sterile applications varied greatly in both design and water quality output. While it has long been widely known that feeding expensive central sterile processing equipment with untreated city water could result in equipment damage due to scale and corrosion, water treatment methods ranged from simple softeners to reverse osmosis (RO) or single-pass deionization. Gradually, sterile processing OEMs began releasing water quality guidelines to maximize equipment longevity by specifying compatible water qualities, focusing primarily on conductivity/resistivity or specific ionic contaminants known to cause corrosion.

There are two key points to understand about legacy central sterile feed water systems:

  • Varied Designs: Systems varied widely in design, ranging from straight pass deionization (DI) to RO, with a focus on removing ionic contaminants.
  • Limited Microbial Control: There was little focus on bacteria, TOC, or endotoxin levels (common in other applications including USP, clinical laboratories, ASTM grade lab water, dialysis and more) until the release of AAMI TIR34 in 2014, which set the stage for ST108.

Introduction of AAMI ST108

AAMI ST108 introduces comprehensive guidelines focusing on microorganism contaminants including bacteria and endotoxin, TOC, and resistivity/conductivity. The ST108 “Critical Water” quality guidelines are summarized below:

Note that ST108 includes separate specifications for “Steam” and “Utility Water.”

Implications for Central Sterile Water Equipment

While ST108 is a recommendation, not a regulation, many proactive central sterile departments are moving rapidly adopting the standard. Unlike previous solutions, ST108-compliant systems are more uniform in design due to the stringent requirements for removing contaminants. An ST108-compliant water system typically includes:

  • Pretreatment + Reverse Osmosis
  • Conical Bottom Storage Tank with Vent Filter
  • Properly Sized Distribution Pump
  • Deionization and/or Electro-deionization (EDI)
  • UV Sterilization
  • Final Filtration
  • Instrumentation for Quality Monitoring

Upgrades may necessitate replacing legacy loops if they are made from incompatible materials or have design flaws like dead-legs, which are insufficient for achieving low bacteria and low endotoxin ultrapure water. Consequently, the cost of these systems can be significantly higher than previous solutions.

Atlas High Purity Water’s Expertise

Fortunately, the ST108 “Critical Water” specification aligns closely with existing high purity water standards such as ASTM Type 1A, CLSI, and USP. Atlas High Purity Water, with its experienced team of applications engineers, is well-prepared to upgrade water systems to meet ST108 requirements. Our expertise ensures that we can effectively address the challenges posed by these new standards.