White Paper

Impact of Water Quality on Sterilisation Efficacy and Equipment Longevity in Australian Healthcare Facilities

August 2025

Disclaimer

This content is provided for information only. The authors make no representation or warranty regarding the accuracy, completeness or currency of the content. No information in this whitepaper should be construed as medical advice. Readers should seek appropriate professional guidance before acting on any information contained in this document. The authors expressly disclaim all liability for any direct or indirect loss or damage arising from the use of or reliance on this information.

Introduction

Water quality is a critical factor in the reprocessing of medical instruments and devices. In Australian hospitals, dental clinics, laboratories, and other healthcare facilities, washer-disinfectors, steam sterilisers (autoclaves), and related equipment rely on water for cleaning, disinfection, and steam generation. Poor water quality can lead to inefficient sterilisation, shortened equipment lifespan, and even patient safety risks. This whitepaper analyzes how key water quality parameters, such as hardness, microbial load, particulate content, and chemical composition affect sterilisation efficacy and the longevity of reprocessing equipment across all Australian states and territories. It also reviews relevant standards and guidelines e.g. Standards Australia and state health departments and recent data from the last five years, and provides examples of challenges and solutions in managing water quality. Clear understanding and proactive management of water quality are essential for healthcare administrators and technical staff to ensure compliance and optimal performance of sterilisation processes.

Summary of Key Points

• Water Hardness: Hard water causes limescale deposits that can diminish sterilisation efficiency, reduce detergent effectiveness, and damage equipment components. Australian facilities must treat water when hardness is high to meet standards e.g. AS/NZS 4187 and AS 5369 that set strict hardness limits.
• Microbial Contamination: Water with high microbial counts or biofilms can re-contaminate instruments and internal water lines, undermining disinfection and posing infection risks. Modern standards mandate extremely low microbial levels e.g. ≤10 CFU/100 mL and absence of opportunistic pathogens in final rinse water to prevent biofilm formation and patient exposure.
• Filtration and Treatment: Achieving the required water quality typically involves multi-stage treatment, sediment and carbon filtration, water softening, reverse osmosis (RO), and disinfection (thermal or UV). These systems must be properly maintained with regular filter changes and membrane cleaning, etc. to consistently meet specifications.
• Corrosive Elements: Water chemistry factors like pH extremes or high chloride content can corrode stainless steel instruments, autoclave chambers, and piping. Guidelines limit chlorides e.g. <0.5 to 10 mg/L depending on use to prevent pitting corrosion. Using corrosion-resistant materials e.g. 316 stainless steel and controlling water chemistry help protect equipment.
• Standards and Compliance: Australian Standard AS/NZS 4187:2014 and the new AS 5369:2023 prescribe water quality requirements for all reprocessing facilities, from large hospital CSSDs to office-based practices. All states and territories enforce these standards, with facilities required to monitor water quality (monthly/annual tests) and implement risk management plans to address deviations. Recent years have seen significant investments e.g. installation of RO systems in dozens of hospitals to meet these water quality standards.

The sections below delve into each of these areas in detail, providing data, examples, and recommendations for healthcare settings across Australia.

Water Hardness: Scaling and Sterilisation Efficiency

Water “hardness” refers to dissolved calcium and magnesium salts in the water, typically measured in mg/L of CaCO3. Hard water is a common challenge in many parts of Australia, with mineral content varying widely by region. For example, Sydney’s water is relatively soft (~50 mg/L CaCO3) and Hobart’s extremely soft (~10 mg/L), whereas Brisbane and Adelaide have much harder water (approaching ~100 mg/L). On a state level, Victoria and Tasmania tend to have the softest water, while Western Australia and South Australia have some of the hardest. These regional differences mean some facilities face greater scaling risks than others if water is not treated.

Effects of Hard Water on Equipment and Processes: Hardness is a primary cause of limescale, the solid deposits of mainly calcium carbonate that form when mineral-rich water is heated. In sterilisers and washer-disinfectors, scale gradually accumulates on heating elements, chamber walls, steam generator coils, jets, and sensor probes. This has several negative consequences:

• Reduced Heating Efficiency: Scale is a poor heat conductor. A layer of scale on heating elements acts as insulation, meaning the heaters must work harder and longer to achieve the required temperatures. This can prolong cycle times or prevent the steriliser from reaching sterilisation temperature reliably, potentially compromising sterilisation efficacy. Heaters coated with scale consume more energy to heat water/steam, raising operating costs and straining components.
• Clogged Pipes and Valves: Mineral deposits can narrow the diameter of pipes and block valves or spray nozzles in washer-disinfectors. This impedes water flow and spray pressure, leading to inadequate cleaning of instruments. In steam generators, scaling inside pipes and valves can cause erratic steam delivery or pressure issues. Facilities have reported cases where pipes became completely occluded by scale within a year when using untreated hard water.
• Sensor and Component Malfunction: Many tabletop autoclaves and some sterilisers rely on water conductivity sensors to detect water levels. Excessively soft (pure) water does not conduct electricity well, but conversely, scale buildup on sensor probes can insulate them and yield false readings. Scale can also cause moving parts like valves to stick. For example, scale deposits in a steam boiler’s level-sensor tube can lead to water level detection failure, risking heater burnout.
• Equipment Damage and Downtime: Over time, heavy scaling can cause premature failure of heating elements, which may overheat due to insulation or short out if conductive deposits bridge electrical parts. It can also lead to gasket leaks or pump strain. Repairing or replacing components such as chambers, heaters or pumps damaged by scale results in costly downtime. For instance, an autoclave less than one year old in the UK had an unexpected heater failure due to severe scale, an incident that could have been prevented with water softening.

Because of these issues, manufacturers often void warranties if failure is due to hard water scale, putting the onus on users to ensure proper water quality. Australian healthcare facilities have recognized that protecting these critical investments and sterilisers costing tens of thousands of dollars requires controlling water hardness.

Impact on Cleaning and Sterilisation Efficacy: Beyond physical damage, hard water can also impair the cleaning and microbicidal process itself. Detergents and enzymatic cleaners used in instrument washers are less effective in very hard water because calcium and magnesium ions can bind to the detergent molecules or form insoluble precipitates. This reduces the detergents’ ability to dissolve soils and can leave residues. In fact, studies have shown that water hardness can reduce the kill rate of certain disinfectants, as Ca/Mg ions neutralize or sequester the active compounds. Inorganic minerals in water may also deposit on instrument surfaces, creating a barrier that shields microorganisms from contact with disinfectants or heat. Thus, overly hard water may lead to incomplete cleaning, spotting on instruments, and less effective high-level disinfection.

Standards and Guidelines for Hardness: Recognizing these risks, Australian standards impose limits on water hardness for various stages of reprocessing. The now superseded AS/NZS 4187:2014 applicable to hospital sterilisation departments and the new AS 5369:2023 both specify that for the initial cleaning stages, water hardness should be ≤150 mg/L as CaCO3. This limit is a maximum; in practice many facilities target lower levels, especially if certain delicate devices are being reprocessed. The standard notes a lower hardness may be needed to avoid damaging instruments. For the final rinse stage e.g. the water used in the final rinse of washer-disinfectors or manual washing before instruments are sterilised, the requirement is much more stringent: ≤10 mg/L hardness (near-soft or demineralised water). Essentially, final rinse water must be very soft to avoid any mineral deposits on instruments or equipment. Additionally, water feeding steam generators for sterilisers must be extremely pure; AS 4187 (Table 7.4) aligns with the European EN 285 standard, requiring feed water hardness of <2 mg/L CaCO3 (virtually zero hardness). Table 1 summarizes some of these hardness specifications alongside other parameters.

Table 1. Key Water Quality Requirements from Standards Australia (AS/NZS 4187:2014 & AS 5369:2023)

Sources: Key parameters extracted from AS/NZS 4187:2014 (Tables 7.2 – 7.4) and consistent with AS 5369:2023 updates.

As shown in Table 1, the standards require a dramatic reduction in hardness from the initial tap water used for cleaning (≤150 mg/L) to the final rinse and steam-generation water (essentially near-zero hardness). In practical terms, this means that most Australian facilities cannot rely on municipal water alone for final rinsing or steam, since even “soft” city water (e.g. 50 mg/L in Sydney) exceeds the 10 mg/L final rinse limit. Treatment (typically water softeners or RO systems) is necessary. The standards also call for monthly testing of water hardness (and chlorides) to ensure ongoing compliance. Many facilities instituted monthly water testing programs after these requirements came into effect; the results often revealed previously unrecognized hardness issues that had to be addressed.

Managing Hardness – Treatment Solutions: The primary solution for hard water is to remove or chelate the calcium and magnesium before the water is used. Common strategies include:

• Water Softeners: Ion-exchange softeners replace calcium and magnesium ions with sodium (or potassium) ions. A softener unit (often installed as pre-treatment to an RO or washer feed) can bring hardness down dramatically and prevent scale. It typically requires a brine tank for regenerating the resin with salt. Healthcare facilities often install softeners if incoming hardness is above ~60 mg/L. Maintenance includes refilling salt and periodic checks.
• Chemical Conditioning: In some cases, feed water can be treated with anti-scalant chemicals or phosphate dosing to inhibit scale formation. However, in sterile services this is less common due to concern about chemical residues on instruments.
• Reverse Osmosis or Deionisation: RO systems inherently remove most hardness as part of overall dissolved solids removal. In fact, if an RO is used (see Filtration section below), a separate softener might still be employed upstream to protect the RO membrane from scale fouling. Deionisation (DI) cartridges or continuous electro-deionisation (CEDI) can also strip hardness along with other ions, yielding very pure water. For example, a high-end water treatment system might use a softener + carbon pre-filter, then RO, and then a polisher like an EDI module to ensure <2 mg/L hardness for a steam boiler.
• Distilled Water: Some dental or lab autoclaves use distilled water (either purchased or produced by on-site distillers) which has extremely low hardness. Distillation is effective but energy-intensive; still, many dental practices use distilled or deionised water for their bench-top sterilisers to avoid scale buildup.

It is important to note that using only pure DI water in certain autoclaves can cause other issues like sensor malfunction or even corrosion of carbon steel boilers. Manufacturers like MES and Consolidated Sterilizers recommend either using distilled water which retains a tiny conductivity or a mix of DI and some tap water to provide slight mineral content for conductivity. For example, one guideline is to fill an autoclave reservoir mostly with DI water but add ~50 to 100 mL of tap water to ensure the water level sensor can detect it. The key is achieving low hardness without eliminating all conductivity needed by the machine’s controls.

In summary, controlling water hardness is vital. By softening and polishing the water supply, facilities prevent scale-related malfunctions, maintain energy efficiency, and ensure that detergents and sterilants work as intended. Given Australia’s geography, where some facilities especially rural or outback hospitals rely on hard bore water, investment in water softening or RO systems has been a necessary step to meet the national standards and protect reprocessing equipment.

Microbial Load: Contamination Risks and Biofilm Formation

Beyond chemical hardness, the microbiological quality of water plays a decisive role in cleaning and sterilisation outcomes. Water used in cleaning stages, final rinses, or steam generation can carry microorganisms such as bacteria or fungi that may contaminate the very items being reprocessed. If not controlled, waterborne microbes can form biofilms in piping and equipment and even survive to be present on supposedly “sterile” instruments or in high-level disinfected devices. This section discusses the risks associated with microbial contamination in reprocessing water and the standards and practices to mitigate those risks.

Risks of Microbial Contamination in Reprocessing: During cleaning, the goal is to remove bioburden such as microorganisms and soil from instruments. If the water itself introduces microbes, it defeats the purpose by increasing the bioburden on devices. For instruments that will later be sterilised in an autoclave, any live bacteria introduced by rinse water would likely be killed by the high heat; however, endotoxins, the toxic fragments of Gram-negative bacterial cell walls are not destroyed by standard sterilisation and can remain on instruments. Endotoxins introduced via rinse water or biofilms are a serious concern because if they enter a patient’s bloodstream even on a sterile instrument, they can cause fevers and inflammatory reactions. For instruments that are not sterilised after the final rinse, notably flexible endoscopes, which undergo high-level disinfection but not steam sterilisation, any bacteria in the rinse water can directly contaminate the device and subsequently infect patients. Indeed, outbreaks of Pseudomonas aeruginosa and other opportunistic pathogens have been traced to contaminated endoscope rinse water in several cases internationally. In Australia, routine water testing in hospitals has occasionally detected organisms like non-tuberculous mycobacteria or Gram-negative bacteria in what is meant to be clean rinse water, prompting immediate remedial actions such as filter changes or system disinfection to prevent patient exposure.

Biofilms are another hidden threat. A biofilm is a community of microbes that adhere to surfaces such as the inner walls of water pipes or filters encased in a protective slime. Once established, biofilms continuously shed bacteria into the flowing water and are extremely difficult to eradicate. Within biofilms, microbes can be up to 1,000 times more resistant to disinfectants than free-floating (planktonic) bacteria. This means that if a biofilm forms in a washer-disinfector’s plumbing or an RO storage tank, even aggressive disinfection procedures might not fully eliminate it. Biofilms in endoscope reprocessor waterlines have been known to defy 0.2 µm filters, with organisms growing downstream of filters and contaminating supposedly filtered water. Common waterborne bacteria of concern include Pseudomonas species, Legionella, Nontuberculous Mycobacteria e.g. M. chelonae, and Achromobacter, all of which have been implicated in infections linked to medical equipment when water systems were the source.

Standards for Microbial Water Quality: Given these risks, the standards impose tight controls on microbial content in reprocessing water. AS/NZS 4187:2014 and AS 5369:2023 mandate regular microbiological testing of water, and specify limits primarily for the final rinse water that contacts devices:

• Total Viable Count (TVC): The total heterotrophic plate count of bacteria in final rinse water should be ≤10 CFU/100 mL for critical processes, this is the limit applied especially for endoscope reprocessors and any final rinse that isn’t followed by sterilisation. For other washer-disinfectors and manual final rinse, a slightly higher limit of ≤100 CFU/100 mL is given, but many facilities strive for the more stringent 10 CFU level as best practice. By comparison, typical drinking water guidelines allow up to 100 CFU/mL, which is 10,000 CFU/100 mL, so the standard for rinse water is hundreds of times more stringent than normal drinking water, essentially approaching sterile water.
• Specific Pathogens: Pseudomonas aeruginosa and atypical mycobacteria, e.g. M. abscessus group must be “not detected” in 100 mL of final rinse water. These organisms are singled out because of their known biofilm-forming, disinfectant-resistant nature and history in device-related infections. “Not detected” effectively means zero tolerance, if even 1 colony is found in 100 mL, the water fails and corrective action is needed.
• Endotoxin: For final rinse water used on devices that will contact the bloodstream or sterile tissues e.g. surgical instruments, implantable device reprocessing, the endotoxin level must be ≤0.25 Endotoxin Units (EU) per mL. This is the same endotoxin limit set for Water-for-Injection in pharmacopoeias, reflecting how critical it is to avoid pyrogenic reactions. For flexible endoscopes, which don’t go into sterile body sites, a higher endotoxin limit of 30 EU/mL is allowed, recognizing the practical challenges in water purification at that scale. Even so, many Australian endoscopy units now aim for the lower endotoxin target by using RO or ultrafiltration for final rinse.

To maintain these standards, monthly microbiological testing of final rinse water is required. This typically includes heterotrophic plate counts and specific tests for P. aeruginosa and NTM (nontuberculous mycobacteria). Some facilities also test for Legionella periodically, especially if warm water systems are involved. Annual endotoxin testing is stipulated as well. If any of these parameters exceed limits, the facility must investigate and remediate immediately. As noted in a 2019 industry report, many Australian hospitals experienced incidents of water quality results exceeding AS 4187 limits once they began routine sampling, highlighting the need for robust response protocols. Infection control and engineering staff had to collaborate on “incident response plans” to address issues like sudden spikes in bacterial counts or positive Pseudomonas findings. Responses include taking affected washers out of service, disinfecting or superheating the water lines, replacing filters, and tracing the source e.g. a dead-leg in plumbing or a depleted UV lamp.

Preventing Contamination and Biofilm: Achieving bacteria-free water is challenging but attainable with a multi-pronged approach:

• Filtration: Most CSSD water treatment systems incorporate sub-micron filters at the final outlets. A 0.2 µm absolute filter can remove the majority of bacteria. However, as noted, biofilm can form on filters or in downstream tubing, so filters must be changed on schedule and downstream tubing periodically sterilised or flushed. In endoscope washers, .2 µm filters on incoming water are standard, and some use ultrafiltration (UF) membranes capable of removing endotoxin as well.
• Ultraviolet (UV) Disinfection: UV sterilisation units are commonly installed in the recirculating loop of RO water systems. UV light at 254 nm can achieve a 4-log (99.99 percent) kill of bacteria without chemicals. In Australian hospitals upgrading for AS 4187, UV systems have been used to continuously treat RO water as it circulates through stainless steel ring mains. UV is effective as long as the water is clear which RO ensures and the UV lamps are maintained which bulbs typically replaced annually.
• Thermal Disinfection of Lines: Many advanced water distribution systems perform auto-flush and thermal disinfection cycles. For example, periodic recirculation of hot water (≥80 °C) through the RO storage tank and loop can kill bacteria and destroy biofilms (thermal shock). AS/NZS 4187 actually requires that RO systems be capable of regular thermal disinfection. Hospitals have implemented nightly or weekly hot flushes of their purified water loops to mitigate bacterial growth and endotoxin buildup.
• Point-of-Use Sterile Water for Critical Rinsing: Some facilities, for critical devices like implants, opt to do a final rinse with sterile distilled water, which comes in single-use containers just before sterilisation, to eliminate any chance of contamination. This is an extra precaution beyond what standards require but is done in certain high-risk reprocessing though costly and labor-intensive.
• Water Quality Risk Management Plan: Australian guidelines encourage each health service to have a Water Quality Risk Management Plan (WQRMP). This plan outlines how water quality is monitored, what preventive maintenance is done to keep microbial quality high, and what trigger-action response plans (TARPs) are in place if an out-of-spec result occurs. Key elements include defined roles/responsibilities, communication pathways, and predetermined corrective actions, e.g. “if any Pseudomonas detected, immediately take these steps…”. By having such protocols, facilities ensure a rapid and effective response to microbial excursions, minimizing downtime and protecting patients.

In summary, the microbial purity of water is just as important as its chemical purity in sterile processing. High microbial loads or biofilms in water can directly compromise patient safety and instrument integrity. Through stringent standards, routine monitoring, and advanced water treatment such as filters, UV, thermal disinfection, Australian healthcare facilities strive to supply ultra-clean, low-bioburden water for all cleaning and rinsing stages. The investment in maintaining this quality is justified by the elimination of waterborne infection risks and the assurance that properly cleaned devices emerge truly free of contaminants before sterilisation or patient use.

Filtration and Water Treatment Technologies for Sterile Processing

Meeting the strict water quality criteria described above is usually impossible with untreated municipal water alone. Whether the facility is a large metropolitan hospital or a small dental clinic, some form of water treatment system is typically required to ensure water is fit for purpose i.e. “instrument-grade” water. This section outlines the filtration and purification technologies commonly used, the standards or recommendations around them, and best practices for maintenance. It also references relevant Australian guidelines for filtration and system design.

Stainless steel piping and valves in a high-purity water distribution system. Modern CSSD water treatment installations use multi-stage systems to achieve the needed water quality. A typical system as recommended to comply with AS/NZS 4187 might include: pre-filtration, softening, activated carbon, reverse osmosis, and a recirculating loop with disinfection. All components in contact with high-purity water are often made of 316 stainless steel, which provides excellent corrosion resistance and prevents leaching of metals or plastics into the water. Plastic pipes can leach organics, and copper pipes can corrode in soft pure water, so stainless steel is the preferred material. Below is an overview of each stage of treatment and related considerations:

• Sediment Filtration: Water entering the system first passes through a coarse filter e.g. 5 micron or 1 micron to remove particulate matter like rust, sand, or pipe debris. This protects downstream equipment, especially RO membranes and valves, from fouling or abrasion. These pre-filter cartridges must be replaced or cleaned regularly (often monthly or as pressure drop indicates). Australian practices often include a micron-rated cartridge or back-washable media filter at this stage.
• Water Softener: As discussed in the hardness section, an ion-exchange softener is commonly used to reduce hardness to <150 mg/L before water goes to washers or RO. The softener typically contains resin that must be regenerated with salt brine. Maintenance involves checking brine levels and periodic servicing of the resin bed. AS/NZS 4187 doesn’t mandate a softener specifically, but meeting the chloride and hardness specs often necessitates one if source water is hard. Some smaller clinics use polyphosphate dosers as an alternative, but these are less ideal for surgical instrument reprocessing due to chemical residuals.
• Activated Carbon Filter: Municipal water in Australia is disinfected with chlorine or chloramine. These chemicals must be removed because chlorine/chloramines can attack stainless steel causing pitting and will also damage RO membranes. Activated carbon effectively adsorbs these and also reduces any organic contaminants. Carbon filters are usually installed prior to RO units. They require periodic replacement or regeneration. If chloramine levels are high, specially activated carbon or longer contact times are needed. Standards specify a chloride limit in water, but that refers to chloride ions; here we are concerned with reactive chlorine which should be zero entering an RO or final rinse stage.
• Reverse Osmosis (RO): RO is the workhorse of water purification in sterile services. An RO system uses a semi-permeable membrane to remove 95 to 99 percent of dissolved ions, as well as virtually all particulate and microbial content. The RO permeate is very low in hardness, chlorides, silica, etc., typically with conductivity well under 30 µS/cm, thus meeting the final rinse and often even the steam feed requirements. AS/NZS 4187:2014 explicitly notes that meeting the final rinse water specs will likely require RO treatment. Many Australian hospitals, in upgrades to meet the standard, installed RO units sized for their washer-disinfectors and sterilisers. For instance, a Queensland hospital might have a centralized RO plant delivering purified water to all sterile processing areas. RO does produce a waste stream (“reject water”), which must be managed and often sent to drain or recycled for non-critical uses. The performance of an RO is monitored via conductivity; if permeate conductivity starts rising, it can indicate membrane fouling or failure. Regular maintenance includes sanitising the RO unit, changing any pre-filters, and occasionally replacing RO membranes, typically every few years. In some cases, double-pass RO is used; the water goes through two RO stages in series, to achieve ultra-low conductivity (<5 µS/cm) for steam boilers, although single-pass RO with good pretreatment usually suffices.
• Deionisation (DI) / Electro-deionisation (EDI): As an optional polishing step, DI resins or continuous EDI modules can further remove trace ions after RO. Some high-end systems incorporate an EDI to consistently achieve Type 1 water quality (resistivity ~18 MΩ·cm, essentially laboratory-grade water). While not always necessary for sterilisation, EDI can ensure that even if the RO performance fluctuates, the final water meets the strictest specs, like the <0.5 mg/L chloride for steam. Maintenance for DI resin involves resin replacement or regeneration service. EDI units are low-maintenance but require power and periodic cleaning.
• UV Disinfection Unit: As described in the microbial section, a UV lamp unit is often placed on the loop to continuously disinfect the circulating pure water. The Australian stainless steel standard case study noted UV in ring mains to ensure compliance with AS/NZS 4187 microbial specs. UV units need their lamps replaced approximately annually and quartz sleeves cleaned.
• Recirculation Loop with Storage Tank: Purified water is usually stored in a closed holding tank, often 200 to 500 liters in a hospital CSSD setup and circulated in a loop to points of use (washers, steriliser feed) by a pump. The loop is typically stainless steel tubing with hygienic design. Constant circulation helps prevent stagnation (stagnant water encourages bacterial growth). The system may include an automatic flush to drain if water has been in the tank too long to ensure freshness. The storage tank often has features like an airtight vent filter and spray ball for sanitization. Periodic tank sanitisation is critical and many systems perform an automatic hot water sanitisation of the tank and loop on a set schedule e.g. weekly. During this, the RO permeate is heated either by an electric heater or by diverting hot water to a disinfecting temperature e.g. 80 to 90 °C and circulated, killing any microbes and helping dissolve biofilm.

The combination of these technologies can reliably produce water that meets or exceeds the standards. For example, a properly designed RO system can bring hardness from 100 mg/L down to <5 mg/L, chlorides from 50 mg/L to <1 mg/L, and bacterial counts to essentially zero, with endotoxin levels in the low EU/mL range. Real-world implementations in Australia have proven this: over 25 hospitals across Queensland, NSW and Victoria recently installed new stainless steel RO water treatment systems to comply with AS/NZS 4187’s requirements. These projects involved replacing old piping with 316 SS tubing, adding RO units, and creating the necessary loop infrastructure. The results were improved water quality and confidence in meeting the microbial and chemical targets, albeit with added responsibilities in maintenance and validation.

Standards and Maintenance Practices: Australian guidelines stress that simply installing treatment equipment is not enough, ongoing maintenance and monitoring are essential to ensure performance doesn’t degrade. Key practices include:

• Regular Monitoring: In addition to the monthly and annual lab tests for hardness, microbes, etc, many facilities use inline monitors. Conductivity sensors on RO permeate give real-time TDS readings; any spike triggers an alarm or divert to drain. Some systems also have continuous chlorine monitors before the carbon filter, so that if chlorine breakthrough occurs e.g. exhausted carbon, the RO is protected and an alarm sounds.
• Documentation and Validation: Under AS/NZS 4187/AS 5369, any water treatment equipment must go through IQ/OQ/PQ (Installation/Operational/Performance Qualification) when installed. This means verifying it meets specs e.g. testing that water quality after installation indeed meets Table 7.2/7.3/7.4 limits. Thereafter, documentation of all maintenance and any incidents must be kept. Health service accrediting bodies often audit these records. The new AS 5369:2023 explicitly calls for a risk-based water quality management plan and documented processes for monitoring and maintenance.
• Filter Replacements: Prefilters (sediment) might be changed monthly; carbon filters perhaps every 6 to 12 months or whenever chlorine breakthrough is detected; 0.2 µm final filters at use-points are commonly changed every 3 months or more frequently if recommended. Not following these schedules can quickly lead to water quality deterioration.
• Membrane Care: RO membranes can last several years if properly protected by prefilters and carbon. Nevertheless, facilities often schedule an annual service where membranes are cleaned using specialised cleaning chemicals that dissolve scale or biofilms or are replaced if their output quality has declined. Membrane performance is also indirectly maintained by ensuring the softener is working any hardness leaking can foul membranes and by avoiding long downtimes. Stagnant water on membranes can breed bacteria; many RO units auto-flush themselves if idle to prevent this.
• Calibration: Instrumentation like conductivity probes, UV intensity monitors, temperature sensors for thermal disinfection should be calibrated or checked periodically for accuracy, as false readings could give a false sense of security.
• Bypass and Emergency Protocols: A well-designed system includes the ability to bypass or take components offline for maintenance. For example, dual alternating softeners so one can regenerate while the other is in service, or a bypass that allows city water to be used in a pinch and not for final rinse, but perhaps for initial wash if RO fails, with appropriate risk assessment. Some hospitals maintain a small supply of distilled water jugs or have an on-site still as a backup for critical needs if the main system is down.

In summary, advanced filtration and purification technology is the backbone of meeting water quality requirements. The combination of physical filtration, chemical treatment, and disinfection ensures removal of scaling minerals, organic and inorganic contaminants, and microbial hazards. However, these systems require diligent maintenance. Australian facilities, guided by standards and industry expertise, have implemented robust water treatment solutions from straightforward cartridge filters in dental clinics to multi-stage RO plants in tertiary hospitals all with the aim of safeguarding their sterilisation processes and extending the life of expensive equipment.

Corrosion and Materials: Effects of Water Chemistry (pH, Chlorides, etc.)

Water that is chemically aggressive can corrode metals and degrade equipment. In sterilisation departments, most components are stainless steel or other corrosion-resistant materials, but they are not invulnerable. Two key chemical factors are pH and chloride content, though dissolved oxygen, iron, and other ions also play roles. This section examines how water chemistry can cause corrosion or other material damage, and how this impacts instruments and machines over time.

Chlorides and Corrosion: Chloride ions from salts like sodium chloride, calcium chloride, etc. are notorious for causing pitting corrosion in stainless steel. Even high-grade 316 stainless can pit if exposed to chlorides at sufficient concentration and temperature. Steam sterilisers often run at 134 °C, a condition that can accelerate chloride attack on steel if chloride levels are high. AS/NZS 4187 acknowledged this by setting a chloride limit of <120 mg/L for general cleaning water, and much lower (<0.5 to 10 mg/L) for final rinse and steam feed (see Table 1 above). If a facility in a coastal area or one using bore water has elevated chloride in its supply, using that water untreated could lead to rust-colored spots or pits in autoclave chambers and on instrument surfaces. These pits are not only cosmetic; they can harbor bacteria and weaken the material. Instances have been reported where surgical instruments especially those made of martensitic stainless steel or containing mixed metals developed brown corrosion spots due to high chlorides in rinse water, requiring costly instrument refurbishment or replacement.

pH Extremes: Water that is very acidic (low pH) or very alkaline (high pH) can also cause problems. Acidic water (pH < ~6) can leach metals like copper, lead, or zinc from pipes if any brass or copper components are present and can slowly etch stainless steel protective oxide layers. Alkaline water (pH > ~8.5) can precipitate minerals (scaling) and also attack aluminum or other materials, though aluminum is rare in sterilisation equipment due to autoclave conditions. The standards specify a relatively neutral pH range for final rinse and steam feed (pH 5.5–8.0 for final rinse, 5.0–7.5 for boiler feed). This ensures water chemistry is not overly aggressive. In practice, RO or deionised water tends to be slightly acidic (CO2 dissolves into it, forming carbonic acid, often bringing RO water pH to ~5.5–6.5). This mild acidity is usually not a concern for 316 SS but could be for lesser grades. Therefore, systems often include pH monitoring. Some RO systems for CSSD have even included a calcite bed (post-RO) to add a bit of alkalinity back if pH is too low, thereby protecting copper pipes in mixing with soft water though copper is ideally avoided, as mentioned.

Other Dissolved Solids: Ions such as iron, copper, manganese if present in water can cause staining on instruments e.g. orange/brown staining from iron. They can also deposit and catalyze corrosion. Iron particles can create galvanic corrosion sites on stainless steel. Standards set iron limits e.g. <0.2 mg/L for final rinse to avoid this. Silicates (>1 mg/L) can leave white deposits and also shield surfaces. Phosphates in water from corrosion inhibitors in mains supply above 0.2 mg/L can leave films and affect detergent action. These all are addressed by using high-purity water for final stages.

Instrument Damage and Longevity: Surgical instruments are expensive and expected to last many reprocessing cycles. If water chemistry is poor, instruments can develop issues like black staining, corrosion, or loss of functionality. For example, high chlorides or improper pH can cause hinge screws to rust or fine edges like scissor blades to pit, making them dull. Hard water deposits, if not removed, can also cause staining and stiff joints. Over time, this shortens instrument life. A notable point is that endoscopes and other delicate devices that get rinsed with water must have that water of high quality to avoid internal corrosion or deposits in channels. Even the autoclave itself: many tabletop dental autoclaves have aluminum chambers or copper tubing, if wrong water is used, these can corrode quickly (which is why manufacturers insist on distilled/DI water for those units).

To mitigate corrosion issues:

• Material Selection: The trend is to use 316L stainless steel for all water contact parts as seen in the new CSSD RO installations since it handles high purity water and elevated temperatures best. Avoiding mixed metals (no copper, brass in pure water lines) prevents galvanic couples and contamination. Plastic components are minimised in pure water lines because certain plastics can degrade or leach; and soft water can even make some plastics brittle over time.
• Controlling Chlorides: This is largely achieved by RO or deionisation, reducing chlorides to single-digit ppm or lower. If a softener is used, which adds some sodium chloride in exchange for hardness, it is usually upstream of RO, so the RO removes the residual sodium and chloride that the softener adds. Thus the final water is very low in chlorides. Monitoring chloride is part of monthly tests; if a spike is seen, it could indicate a problem like a malfunctioning RO bypass or contamination ingress.
• Maintaining Neutral pH: If RO permeate pH is too low, facilities can blend a tiny fraction of filtered tap water or implement a re-mineralisation as mentioned. However, blending is risky unless carefully controlled, as it could raise other parameters. Most rely on the natural buffering of the water system and frequent usage. Stagnant RO water can drop in pH as CO2 diffuses in; keeping water moving and covered mitigates this.
• Preventing Fouling: Deposition of unexpected substances can create sites for corrosion. For example, leftover chloride or cleaning chemical residue on an instrument that goes into an autoclave can cause “rainbow” staining or corrosion spots on that instrument and even on the chamber over time. Thus, thorough rinsing with high-purity water after cleaning is key to remove all chemical residues that might corrode instruments during sterilisation. This also ties back to water purity: if the rinse water is pure, it helps rinse away any harsh chemicals like alkaline detergent and then evaporates cleanly in the autoclave without leaving deposits.

In essence, water chemistry must be balanced, not too impure to avoid scale and deposits, but also not aggressive to materials. The Australian standards’ limits for chlorides, pH, and other ions were set with corrosion prevention in mind. By adhering to these limits and using appropriate materials, facilities can greatly extend the life of both their instruments and their processing equipment. One positive outcome noted from the recent upgrades is that new stainless steel RO distribution systems have eliminated the corrosion issues that sites with old copper plumbing were experiencing, where soft, pure water had been leaching copper and causing greenish residues and pinhole leaks. Using the correct grade stainless and keeping water within specs ensures a durable system with minimal corrosion-related downtime.

Regulatory Guidelines and Australian Context

Achieving excellent water quality in sterilisation is not only a best practice but a requirement codified in guidelines and standards. In Australia, the primary standards have been AS/NZS 4187:2014, Reprocessing of reusable medical devices in health service organizations and the recent AS 5369:2023, which supersedes both AS/NZS 4187 and AS/NZS 4815 (the latter was for office-based healthcare facilities). Compliance with these standards is expected in all states and territories, supported by state health department directives and accreditation bodies. This section provides an overview of key regulatory expectations, recent updates, and examples of how various jurisdictions have implemented them.

Standards Australia, Water Quality Requirements: The standards have clearly elevated the importance of water quality. AS/NZS 4187:2014, especially after Amendment 2:2019, introduced the detailed water quality tables (7.2 to 7.4) we’ve discussed. It required health service organizations to test their water and, if necessary, treat it to meet those specs. There was a transition period given and hospitals were expected to achieve full compliance by December 2021. Many states e.g. NSW, Victoria, Queensland had issued guidance that their public hospitals needed to budget and implement necessary water treatment upgrades by this deadline. Compliance was often checked as part of hospital accreditation surveys in 2020 to 2021.

In primary care settings such as general practices or dental clinics, the older AS/NZS 4815:2006 had looser requirements, but the new AS 5369:2023 brings these in line with the hospital standard. As of late 2023, AS 5369:2023 is the unified standard for all settings, meaning even a small dental office is expected to consider water quality for their sterilisers and if applicable instrument washers. AS 5369 specifically forbids use of poor-quality water, it permits drinking water for cleaning only if it’s of acceptable hardness, etc. and then sets the same minimum specs for hardness, chloride, final rinse pH, conductivity, etc. as in 4187. There is now an expectation that every practice obtain information about their local water supply quality and perform a gap analysis to see if additional treatment is needed. For instance, a dental clinic in Adelaide with ~100 mg/L hardness water should recognize that using that water straight in their autoclave will cause scale and likely fail the standard, so they should install at least a countertop distiller or DI filter. The new standard pushes for a risk-based approach, e.g., if a facility’s water slightly exceeds one parameter, they must assess the risk to their devices and patients and decide on mitigation as it could be as simple as using a filter carafe for small volumes or as complex as a full RO install.

State Health Department Guidance: All states and territories generally refer to the national standards, but some have issued additional guidance or templates. For example, Western Australia Country Health Service (WACHS) has a detailed procedure for water quality management that reiterates the need for compliance with AS 5369 and provides local tools like a “Water Quality Requirements” template and testing schedule. It also nicely summarizes the rationale for each water factor such as hardness, heavy metals, microbial, etc. in plain language. SA Health and Queensland Health have similarly ensured their infection control or facilities guidelines incorporate water quality checks. In many cases, state-level infection control auditors have asked for evidence of water testing and maintenance as part of licensing inspections.

Notably, the NHMRC’s Australian Guidelines for the Prevention and Control of Infection in Healthcare (2019) also mention that water quality must be suitable for the reprocessing stage and reference AS/NZS 4187 for specifics. While this NHMRC document is advisory, it is widely followed and further cements that using poor quality water in sterilisation is not acceptable.

Enforcement and Incidents: If water quality standards are not met, facilities risk non-compliance citations and, more importantly, patient safety incidents. There have been a few reported instances of instruments with staining or residuals being traced back to poor water quality. For example, a large hospital in NSW found high endotoxin levels in its final rinse water during commissioning tests, it turned out a newly installed RO unit had a microbial contamination. The issue had to be rectified before any surgical packs could be released, causing delays. In another case, a rural hospital’s steam sterilisers suffered repeated heating element failures; investigation revealed the feed water softener wasn’t regenerating properly, allowing excessive hardness, once fixed, the failures stopped. These cases underline why regulators are keen on preventive maintenance and routine monitoring.

In response to challenges, there has been knowledge sharing through professional bodies like the Sterilizing Research & Advisory Council of Australia (SRACA) and the Australasian College for Infection Prevention and Control (ACIPC). The ACIPC 2019 conference, for instance, featured presentations on water quality incidents and response protocols, as well as case studies like managing water quality in rural settings where resources are limited and water may be sourced from small treatment plants or rainwater tanks. One key learning from rural hospitals in WA was the need for backup systems, e.g. if RO fails and parts take time to ship, having a contingency like a portable DI tank can save the day.

Dental and Laboratory Facilities: In smaller facilities, regulatory oversight is somewhat lighter e.g. dental practices are often just expected to follow ADA Guidelines and AS 4815/5369, usually checked when accreditation or inspections occur. Nevertheless, the principles remain the same. The Australian Dental Association (ADA) guidance echoes that autoclaves should be fed with distilled or deionised water to minimise scaling and ensure proper sterilisation. Many dental offices use inexpensive countertop RO units or simply buy distilled water for use in autoclaves. For laboratories e.g. pathology labs sterilising media or waste, there is less direct regulation, but any lab in a hospital setting would fall under that hospital’s compliance with AS 4187/5369. Thus, they too have to meet water specs if their autoclaves or glassware washers interface with the central water system.

In summary, all Australian jurisdictions align on the expectation of high water quality for sterilisation and disinfection processes. The push in the last 5 years to implement AS/NZS 4187’s water requirements has led to tangible improvements: many facilities now have water quality that consistently hits the marks and they have the test data to prove it. This was a significant investment, financially and in staff training but it has elevated the reprocessing standard to world’s best practice. Going forward, facilities must remain vigilant: maintaining water systems and quality is an ongoing task. With the new AS 5369:2023 extending these requirements across all healthcare facilities large and small, Australia has a comprehensive, nationally consistent framework ensuring that whether a patient’s instrument is sterilised in a major Sydney hospital or a small clinic in the Outback, the water used will not be the weak link in the chain of infection prevention.

Conclusion and Summary Findings

Water quality directly affects both the efficacy of sterilisation and the durability of reprocessing equipment. Australian healthcare facilities have embraced the fact that controlling water hardness, purity, and microbial content is a fundamental part of modern infection control. Key conclusions from this analysis include:

• Hard Water Mitigation: Hardness in water, if unchecked, causes scaling that can compromise steriliser performance and significantly shorten equipment lifespan. Ensuring water hardness is reduced below recommended thresholds ≤150 mg/L for cleaning, and near-zero for final rinse/steam is essential. This is achieved through softening and high-purity water production. Facilities that invested in water softeners and RO systems have seen reductions in limescale problems and equipment failures, translating to fewer repairs and more reliable sterilisation cycles.
• Microbial Safety of Water: The presence of microorganisms or biofilms in water used for cleaning or rinsing can lead to contaminated instruments and potential patient infections. By enforcing ultra-low microbial limits e.g. <10 CFU/100 mL and requiring action when any pathogens are detected, standards have driven facilities to implement robust disinfection measures such as UV, thermal flushes, filtration. The result is water that effectively does not add bioburden to the cleaning process, a critical factor in achieving true sterilisation. Hospitals now treat water quality failures with the same urgency as a failed steriliser biological indicator, reflecting how central it is to patient safety.
• Comprehensive Filtration and Treatment Systems: Multi-stage water treatment such as sediment filtration, carbon, softening, RO, UV, etc. is now common in Australian CSSDs and many larger clinics. These systems ensure compliance with chemical and microbial specifications and protect expensive equipment from corrosion or fouling. Maintenance of these systems has become a routine part of sterile services operations. Staff are trained to monitor water quality parameters and perform or arrange regular servicing. This professionalisation of water management often via Water Quality Risk Management Plans has markedly improved consistency, clean devices and functioning machines are not jeopardised by unseen water issues.
• Corrosion Prevention: Attention to water chemistry, controlling chlorides, pH, and other ions, prevents insidious corrosion that can ruin instruments and infrastructure. By using high-grade materials and maintaining water within narrow chemical ranges, facilities avoid pitting, rust, and strange deposits. This not only preserves instrument integrity so surgical tools remain sharp and safe through many cycles, but also means sterilisers and washers can reach or exceed their expected lifespans without costly chamber replacements or overhauls due to corrosion.
• Regulatory Compliance and Improved Outcomes: The concerted effort across all Australian states to meet AS/NZS 4187 and now AS 5369 has led to a high level of compliance by 2025. Many healthcare administrators allocated capital funding for water treatment upgrades, recognising that non-compliance was not an option. The outcome is a nationally uniform standard of water quality in reprocessing departments. A hospital in Perth and one in Brisbane are both treating their water to similar levels, guided by the same evidence-based requirements. This consistency is particularly important as staff move between facilities or when audits occur; everyone speaks the same language of water quality metrics and targets. In the end, the patients benefit: the instruments used in their care are cleaner, free from residues and pyrogens, and sterilised in machines that operate at peak performance.

In conclusion, water may be an often “invisible” component of the sterilisation process, but its quality underpins everything. As this whitepaper has detailed, ensuring high-quality water, soft, pure, and sterile or near-sterile, is indispensable for effective sterilisation and for the longevity of the washers, sterilisers, and autoclaves that healthcare depends on. The Australian experience in the last five years demonstrates that with clear standards, institutional commitment, and appropriate technology, the challenges of water quality can be successfully managed, resulting in safer outcomes and more resilient reprocessing operations. Facilities must continue this vigilance: water quality management is not a one-time project but a continuous responsibility. With ongoing attention and adherence to guidelines, Australian healthcare providers can be confident that water will remain a helper, not a hindrance, in delivering safe and sterile instruments for patient care.

Sources

1. Standards Australia, AS/NZS 4187:2014 (Amd 2:2019) - Reprocessing of Reusable Medical Devices in Health Service Organizations, key water quality requirements.
2. Standards Australia, AS 5369:2023 - Reprocessing of Reusable Medical Devices in Health and Non-Health Care Settings, updated water quality clauses.
3. Gastroenterological Nurses College of Australia - Summary of AS/NZS 4187:2014 water testing requirements.
4. ASSDA Case Study, “Raising the standard with stainless steel” - Implementation of RO water systems for AS/NZS 4187 compliance.
5. WACHS (WA Health) - Water quality in reprocessing procedure, on effects of hardness, heavy metals, microbial load, endotoxins.
6. Southland Filtration (Dr. S. McCaw) - Microbial Water Quality in Reprocessing, on how hardness and biofilms affect disinfection.
7. ACIPC Conference 2019 - Abstract on water quality incident response.
8. ACIPC Conference 2024 - Case study on rural CSSD water challenges.