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What Hospitals Need to Know: Using Water During Processing of Medical Devices
Infection Prevention

What Hospitals Need to Know: Using Water During Processing of Medical Devices

Every day, hospitals’ central sterile processing teams rely on water as they clean and sterilize a variety of medical devices. In this blog, ECRI outlines general considerations to support safe and effective water preparation and use.

Water Quality Categories

There are three categories of water used to process medical devices. The first is utility water.  Utility water is suitable for use for point-of-use treatment of a device immediately after patient use, but is not drinking water quality.  Utility water is suitable for use for point-of-use treatment of a device immediately after patient use. The temperature of water used for this purpose should not exceed 45C/113F to prevent coagulation of blood and fixation of proteins on the instrument. This water is used for most parts of medical device processing—including flushing, washing, and intermediate rinsing. The notable exception is the final rinse.

The second category is critical water, which undergoes an extensive, multistep process to adhere to stringent water quality measurement values. For example, critical water must have a pH of 5.0 to 7.5 at a temperature of 25 degrees Celsius; total alkalinity of less than 8 mg calcium carbonate (CaCO3) per liter; and bacteria of less than 10 colony-forming units per milliliter (CFU/mL). Critical water is used for final rinse after high-level disinfection (HLD), final rinse for critical devices prior to sterilization, and feedwater for process team production.  

The third category is steam—vaporized water produced by a central boiler or generator/heat exchanger near the sterilizer. Steam quality and purity are tested as condensate, and both affect sterilizer performance.

Measuring Water Quality

Multiple metrics are used to measure performance qualification levels of water quality for medical device processing:

  • pH specifies the acidity or basicity of an aqueous solution. Extremes in pH level affect device surfaces and can interfere with cleaning agents.
  • Alkalinity is a measure of dissolved alkaline solids (for example, bicarbonate, carbonate, and hydroxide). When high alkalinity is present, it increases the likelihood of hard-water salts forming scale on instruments, which can stain or corrode them.
  • Water hardness is similar to alkalinity, as they both come from natural sources. Water picks up minerals as it moves through rocks on its way to rivers and lakes. When limestone and dolomite dissolve in water, one half of the molecule is calcium or magnesium (the “hardness”). The other half is carbonate (the “alkalinity”). Thus, the level of water hardness and alkalinity in a place will be similar. However, they are very separate measurements with quite different importance.
  • Elevated levels of bacteria may increase the risk of patient infections and pyrogenic reactions. For potable water, the safe level is less than <500 CFU/mL.
  • Endotoxin is a measure of gram-negative bacteria. Endotoxin testing is necessary only for the final rinse after high-level disinfection.
  • Total organic carbon (TOC) is a measure of efficacy in removing organic material.
  • Conductivity measures the total number of ions (that is, electrically charged particles). This is a broad measurement of impurities in a sample and is used as a proxy for total dissolved solids. Ionic contaminants include aluminum, copper, iron, manganese, sulfate, and zinc, among others. Many ionic contaminants can corrode stainless steel, contribute to scale, leave residue, and/or interact with cleaning chemicals.
  • Total hardness is a measure of calcium and magnesium levels, which affect residues on devices. “Hard” tap water has calcium and magnesium levels of greater than 150 parts per million (PPM). 

Considerations for Cleaning Instruments 
As previously noted, different water quality categories are used depending on the process at hand. For point-of-use treatment, utility water is acceptable (other than in the operating room, where sterile water is best). Avoid hot water to prevent coagulation of blood and fixation of proteins. For the cleaning process, utility water is acceptable (if it meets requirements, tap water also can be used  ). In either case, it must be compatible with cleaning agents. Teams can rinse with utility water, but for the final rinse, they must use critical water.

Mechanical cleaning by washers and washer-disinfectors

There are several considerations for mechanical cleaning of medical devices. Washers and washer-disinfectors need values for hot water, cold water, and critical water (which may be optional). Key water factors include pH level, water temperature as determined by cleaning agent instructions for use (IFU), ionic contaminants, microbial level, and bacterial endotoxin. Another key factor is water hardness—which, ideally, will be less than 150ppm CaCO3—though some equipment may have internal water softening systems.

Process Water Quality to Use
Initial rinse Utility water at or before 25 degrees Celsius
Wash Utility water (temperature affects cleaning agent effectiveness) 
Post-wash rinse Utility water
Thermal disinfection Critical water is ideal but not required if there is a final rinse
Duration and temperature vary by IFU 
Final rinse Critical water

Ultrasonic cleaners and liquid chemical high-level disinfection

For ultrasonic cleaners, consult IFU regarding water. For liquid chemical high-level disinfection, dilute liquid chemical if required, and use utility water or critical water based on IFU. For final rinse after HLD, use critical water.

Water Treatment Methods


Tools and techniques for water pre-treatment include:

  • Greensand depth filter for feedwater with elevated levels of iron and/or manganese
  • Water softener for hard water, which will exchange calcium and magnesium ions with sodium ions and yield soft water (Note: This can be a vessel of resin with sodium ions attached or automatic regenerative softeners in brine tanks.)
  • Submicron filter
  • pH adjustment
  • Activated carbon, which is common as pretreatment for reverse osmosis (RO) and deionization (DI)
  • Metabisulfite injection, which removes chlorine and chloramines


There are several techniques for purifying water—including RO, DI, cation exchange resin, anion exchange resin, distillation, and ultrafiltration.

Distribution , Storage, and Final Treatment

At the conclusion of the water treatment process, water can be stored, distributed, and further treated via UV, ozone, steam/hot water, or chemical disinfection.

When it comes to water purification, reverse osmosis systems are widely used Reverse osmosis removes dissolved inorganic solutes, bacteria, and bacteria endotoxin via feeding water osmosis across an RO membrane.

Deionization is an ion exchange process that removes both anions and cations. Deionization is good for removing ionized contaminants but cannot remove non-ionized substances, such as bacteria or endotoxins. This approach is usually used together with RO or as a standby process if RO fails. Note that DI tanks can exhaust and need replacement.

Finally, distillation is the oldest and simplest method of purifying water. Steam from boiled water is condensed, removing inorganic salts, bacteria, and viruses. It works best with pretreatment.

Other Considerations

When faced with unusual circumstances, hospitals’ sterile processing teams must address additional nuances. Examples include resuming operations following construction or extended shutdown; extended boil-water alerts and steps to take once such alerts are lifted; and quality assurance checks.

Learn more about how ECRI can support you with evidence-based, multi-disciplinary consulting, proactive assessments, and infection-related investigations.