Sterilization Central: Water Quality in Medical Device Processing: The Power of Prevention

It may be useful to remember at this stage that water quality can be defined as a descriptor of the levels of various impurities present in water.¹ For processing, this can include chemicals, microorganisms, and other materials that may (or may not) be considered safe for potable (or drinking) water but may not be appropriate for use in processing. We can consider negative effects of these impurities in two different areas: chemical and microbiological.

Chemical risks include device or equipment damage, the creation of precipitates on surfaces, and the transfer of toxic levels of chemicals to patients.^1,2,7,8 Common examples include the presence of chlorides (or other oxidizing agents) in the water and levels of water hardness (Figure 2). Chlorides are commonly found in potable water, as chlorine or chlorine-releasing agents are widely used to disinfect (sanitize) and preserve potable water. But they also react with metal surfaces to cause damage (e.g., corrosion), thereby allowing rust (brownish-red deposits of iron oxides) to develop and, when concentrated locally on a surface, pitting or cracking to occur. For this same reason, saline (a sodium chloride solution) is not recommended for cleaning metal devices. Repeated exposure, especially from water that is heated (e.g., for disinfection or sterilization), will damage devices over time and reduce their expected life.

Remember: If it is in the water or steam, it can end up on the device. Although the visual signs can be remediated, the underlying damage may still be present and can affect safe use and functionality of the device. These microscopic changes also may result in areas on the device surface that may not be decontaminated. A very common precipitate, especially on heating or drying, is hardness (i.e., the presence of dissolved calcium and/or magnesium salts in water). Hardness often is seen as white or chalky precipitates on surfaces. These effects can reduce the lifetime of processing equipment and devices, especially if they are constantly remediated using acid solutions that will dissolve deposits but also can damage surfaces. The introduction of such precipitates into patients, especially when the device is for surgical use, can potentially lead to complications. Other types of chemicals (e.g., copper, iron, manganese) can present a patient risk at higher concentrations and can lead to obvious signs of staining or tarnishing of the device over multiple uses.

Although many of these chemical risks can be seen with the naked eye over time, the microbiological risks typically are not visible. Microbial contamination during the rinse procedure is the biggest risk posed by improper water quality, especially for noncritical or semicritical devices that are disinfected with chemicals. In some cases, even when the water is treated (e.g., filtered) but not correctly maintained, it can be recontaminated due to the presence of bacterial biofilms in the intervening water lines.⁹ Also, certain types of bacteria that grow well in water (gram-negative bacteria) can release endotoxins that can lead to patient harm; these toxins are not inactivated by thermal disinfection or sterilization.

During sterilization processes involving moist heat, controlling water quality for the appropriate chemical, microbiological, and endotoxin levels is critical to ensuring that devices that have been exposed to steam are safe for patient use.¹⁰ The hidden effects of water quality that can influence processing also include interference with the effectiveness of chemicals used for cleaning and chemical disinfection and shielding microorganisms from sterilization processes.^1,7,8

Although certain visual indicators (e.g., being cloudy or discolored) may pertain to the quality of water, the appearance of the water will not provide enough information to meet water quality requirements for processing. Testing is required to determine whether chemical and/or microbiological contaminants may be present. Unfortunately, one test does not provide all of the information needed; however, recommended testing is simple and cost effective to perform routinely (Table 1).¹

It is important to remember that various sources of water may be used at different stages in processing, so consider identifying and testing all sources. Cold and hot water may be from the same source, but these qualities can be modified due to treatment at the facility (e.g., purification methods, heating, circulation in pipes to the point of use). Although finding different levels of contaminants in hot versus cold water is not unusual, and water may be treated (e.g., via a water softener, by passing through a filter, through purification by reverse osmosis), this does not mean that it is fit for the intended use. Of note, the best place to test water is at the source of where it is used (e.g., sink, washer-disinfector).

Conducting all tests listed in Table 1 may be unnecessary—the selection of the tests needed to demonstrate adequate water quality will depend on the intended use. Clearly, the level of risk associated with water used for cleaning, final rinsing following chemical disinfection, or thermal disinfection or steam generation for sterilization will be different.

With water quality analysis completed, the next step is understanding the results and considering whether taking further action is needed. For the processing of devices, two general categories of water are recommended: utility and critical.¹

Utility water can simply be potable water (or water directly from the tap), but the quality of tap water at the point of use needs to be determined. Tap water quality can vary considerably based on geographical region, time of year, distribution systems, and the effects of different treatment processes/chemicals up to the point of use. Therefore, additional treatment may be necessary to meet the quality requirements for this category. A good example is water hardness (e.g., very hard water has been reported in many states in the central and southern United States¹¹), and water softening may be required to meet recommendations for processing.

Critical water, as the name suggests, is used for higher-risk stages of processing, such as final rinsing, thermal disinfection, and steam generation. To obtain and maintain this quality, water must undergo extensive treatment to reach the required specification (e.g., using a reverse osmosis treatment process to remove chemical and microbiological contaminants to low levels).¹ The chemical and microbiological recommendations for the quality of these water categories are further defined in AAMI standards and guidance.^1–5

These categories of water are required at different points in device processing. Utility water can be acceptable for noncritical device use, but if used as a final step in processing these devices, one must consider the impact of the presence of high levels of microorganisms that can be present in uncontrolled water and may pose a potential risk to those handling the device prior to or during patient use (even if gloves are used). Utility water is acceptable for initial cleaning processes with semicritical and critical devices (e.g., flushing, washing, rinsing), but as the device gets closer to the end of the processing cycle, critical water should be used in the final rinse steps. When using equipment that performs this step in the process (e.g., washer-disinfector, ultrasonic bath), critical water should be supplied to the equipment for final rinsing.^1–4 Disinfection (thermal or rinsing following chemical treatment) or sterilization processes that use steam also should be conducted with critical water as a source. As stated above, it is important to consider testing the water (or steam) at its point of use to ensure it is acceptable.

For many microorganisms, water is a suitable environment for growth. Care should be taken to avoid conditions in which water can stagnate or introduce additional microorganisms prior to use. A good example is using filters to remove bacteria, but then the water is contaminated during transport through the water line to the site of use.⁹ It is important to remember that gram-negative bacteria can survive and grow in water (even purified water). These bacteria are important sources of infection and can generate endotoxins that may lead to other patient risks.

In addition to standards and guidance, requirements from processing equipment, chemical, and medical device manufacturers need to be considered. These requirements should be provided through labeling on the product and/or provided with the product (instructions for use). For example, manufacturers may provide recommendations on the quality of the water used to dilute cleaning chemicals or disinfectants to ensure optimum effectiveness, acceptable hardness or proper chloride levels for water used in washer-disinfectors or ultrasonic systems, and to indicate requirements for steam generators. Most device manufacturers will recommend essential standards and guidance for ensuring device safety.

The chemistry of water is complex and can interact with various device and equipment materials. These effects can become visible on devices over time, initially eroding materials on a microscopic level before damage becomes visible to the naked eye.^1,7,8 Figure 2 provides examples of typical visual indicators related to water quality. These can become obvious on the surfaces of washer-disinfectors and steam sterilizers over time. They will appear rapidly on any heating elements in these or associated systems.

If frequent cleaning or acid washing of the inside surfaces of washers, sterilizers, or associated heating systems is required, then the water treatment system may need to be checked or updated to prevent issues. Delaying this can lead to premature aging or damage to equipment, increasing costs long term to the facility. It is important to note that this may also cause concern for the presence of residuals on devices. Visual indicators can signal problems and the need to take action.

The first priority is to meet patient safety requirements and minimize risks of device/equipment damage or cross-contamination during processing. The steps described above can help to address this priority. The next priority is being ready for audit inspections, as water quality is an essential requirement for device processing as defined in associated standards.^2–4 Health-care facilities also must be ready to understand the maintenance of the water system and to actively monitor for changes in water quality that may occur unexpectedly. This is where the concept of “it takes a village” comes into play, as it is a means of ensuring that the support team is engaged and ready to respond to water quality issues. Not being ready to react can lead to the use of the processing facility being suspended.

The time invested in water quality can help control costs, especially when damage to devices or processing equipment can occur over time. Remediation of these effects can be costly, be time intensive, and result in increased patient risk. Although refurbishing the obvious signs of damage on a visual level may be possible, at a microscopic level the effects of the damage can lead to inadequate cleaning and disinfection/sterilization, can pose toxicity risks, and can increase the risk of device malfunction or damage during use.