Christopher Hall, Director of Aquacure Water Treatment, discusses the importance of selecting the right water treatment process for each use, and explains why Reverse Osmosis (RO) is not always the most suitable option for endoscope reprocessing.

Clearing muddy waters

Endoscope reprocessing uses water. But what type of water is required? What water quality, exactly? What water treatment processes are appropriate for this application?

Just as endoscope reprocessing methods and requirements are different from many other Reusable Medical Device (RMD) reprocessing requirements, the feed water requirements for endoscope reprocessing are different from those for RMD reprocessing in the Central Sterile Services Department (CSSD) of a Health Service Organisation (HSO).

There are differences in temperature and usage patterns. Under the current Australian Standard (AS/NZS 4187:2014 Amd2:2019), there are differences in the water quality requirements, too. This means that the feed water supply to the Endoscopy Department Cleaning Room, and to an ‘Automated Endoscope Reprocessor’ (AER), should be considered separately from the water used in the CSSD.

Some are using Reverse Osmosis (RO) even at times when it may not be required. There are capital and maintenance cost implications for the HSO, as well as performance implications in the Endoscopy Department. Cutting straight to the chase, in many cases, contrary to common misconception, RO may not be required for Endoscopy. In some cases, RO might even be better avoided.

How to know?

Water from different sources can differ significantly in quality. Different HSOs can have different feed water, and different water quality requirements for different purposes within each Health Service Organisations (HSO). Although the feed water quality at a particular site may be satisfactory for some uses, it would rarely be suitable at any site for all uses within the HSO without further treatment.

Some of the applications with different water quality requirements include ‘hospital drinking water’ including water for an immunocompromised patient population (control of Legionella and other water quality hazards), water for haemodialysis, water for laboratory use and, of course, water for reprocessing RMDs.

RMD reprocessing requires special consideration. Within that area, there are two distinct sub-categories for water quality requirements: CSSD and Endoscopy. The Australian/New Zealand Standard AS/NZS 4187:2014 specifies the different water quality requirements for RMD reprocessing in each department.

Use of water is a fundamental part of RMD reprocessing. As noted in the Standard, “The quality of water used at all stages in the cleaning process is critical to the successful outcome of the process”[1]

The latest version of the Standard identifies three water types required for RMD reprocessing: ‘cleaning process’ water, ‘final rinse’ water (separate requirements for CSSD and for Endoscope Reprocessing) and water for ‘clean steam’ (not required in endoscope reprocessing).

Endoscope reprocessing is a different process from other RMD reprocessing, and the water requirements differ accordingly. It has its own ‘Final Rinse’ table in the Standard.

There are also specific requirements for water temperature: Endoscope reprocessing uses warm water. This is significant. Water temperature influences other water quality characteristics and options for water treatment and water delivery to the AER.

Cleaning Process Water

The Standard[2] specifies maximum limits for Total Hardness (150mg/L) and Chloride (120mg/L) in the Cleaning Process feed water. Total Hardness is a concern for build-up of scale. Chloride is a concern for corrosion. The effects of both can be amplified by other water chemistry characteristics including pH and temperature.

Both Hardness and Chloride at some level are common in drinking water supplies, though, fortunately, often below the specified maximums. In many parts of Australia, including the three largest capital cities—Sydney, Melbourne and Brisbane (most days)—the levels of Hardness and Chloride are usually low enough that no additional water treatment would be required to comply with this part of the Standard. Some other areas of Australia, on the other hand, are not so fortunate, with Hardness and/or Chloride levels routinely above the maximum limits of the Standard.

Total Hardness

Total Hardness (TH as CaCO3) is often easily controlled with a Water Softener[3] treating the incoming drinking water supply. A Water Softener can provide a very good Return-On-Investment (ROI) even in areas where Hardness is below 150mg/L through efficiencies related to preventing scale. Water Softening is well proven technology that is simple and relatively low cost.

From discussion with some AER manufacturers and CSSD/Endoscopy consultants, there appears to be broad consensus that Water Softening is often beneficial in endoscope reprocessing. For more information about the pros and cons of Water Softening for a specific site and water source, it is best to contact a water treatment specialist.


Chloride is another matter.

Chloride corrosion of stainless steel is a relevant concern in RMD reprocessing. It is affected by the chloride concentration, other water chemistry (temperature, pH), and the type of stainless steel. If the Chloride concentration levels are regularly above the Standard’s maximum (120mg/L) then it’s likely that at least partial desalination of the feed water will be required. This would require a more complex water treatment system, likely including Reverse Osmosis. There are flow-on effects with downstream plumbing and processes.

Fortunately, many Australian drinking water supplies have only very low levels of Chloride – well below the specified maximum of 120mg/L. However, the ADWG allow for Chloride levels of up to 250mg/L, and some drinking water supplies – e.g. Perth, some regional areas – can regularly have Chloride levels above the AS4187 Cleaning Process water requirements. If an Endoscopy Department’s water falls into this category, then they will likely require a water treatment specialist company to provide a suitable customised solution to suit site-specific feed water characteristics.

Final Rinse Water

There was uncertainty in some quarters about the water quality requirements, including ‘Final Rinse’ requirements for endoscope reprocessing when AS/NZS 4187:2014 was first released. The first version of the 2014 Standard included one table only for all Final Rinse water: Table 7.2 (2014).

Amendment 2 (2019)[4] provided further clarification, with updates to the CSSD requirements, and the different Final Rinse water quality requirements for endoscope reprocessing listed in Table 7.3. Meeting the requirements for endoscopy is different from meeting the requirements relating to CSSD use.

Whereas the CSSD requirements include a list of limits for various chemical/ physical parameters in the feed water and a couple of microbiological parameters (TVC and Endotoxin) only, the endoscopy requirements focus on the stringent microbial control requirements in the feed water required for endoscope reprocessing, leaving the question of other aspects of water purity (chemical purity, including dissolved solids etc) to the recommendations of the AER manufacturer.

Table 7.3: Chemical Water Quality

A survey of the recommendations from three Washer-Disinfector (WD) – Automated Endoscope Reprocessor (AER) – manufacturers[5] indicate that ‘potable water’ is their minimum requirement for chemical purity, but that in many cases additional filtration and/or Water Softening may also be required.

There seems to be less clarity or consistency around the suitability of demineralised water and Reverse Osmosis (RO). This may be because the suitability of water treatment processes such as RO should be considered on a case-by-case basis, and a best-fit solution devised according to site-specific needs in partnership with an experienced water treatment specialist.

Water Temperature

A specific, stable feed water temperature is usually a critical AER requirement, for both ‘Cleaning Process’ and ‘Final Rinse’ water. This is relevant for cycle times in the AER, the water and product chemistry used in AER cleaning and disinfection processes, and the temperature limitations of the endoscope itself.

The automated reprocessing of endoscopes occurs at low temperatures. This is a key difference from most RMD reprocessing in CSSD (which uses high temperatures).

The use of Reverse Osmosis (RO)

We’ve observed that sometimes a water treatment system including RO is considered or installed for endoscope reprocessing when it may not necessarily be required to comply with the Standard. This can have significant cost implications for the HSO.

Reverse Osmosis (RO) is a water treatment process used for removing most of the dissolved solids from water. It does not work in isolation; an RO machine is usually one part only of a complete Water Treatment Plant, which will typically also include filtration, Water Softening, de-chlorination, and other water treatment processes which can vary depending on the feed water characteristics and the treated water requirements.

RO is a process, not a water type. Some refer to the product of this process as ‘RO water.’ A better general description of the water type in this context is ‘demineralised water’. ‘Demineralised’ water, however, is not the same as ‘sterile’ water.

RO is primarily a desalination/demineralisation process. Controlling microorganisms is a different function from desalination/demineralisation, often requiring different processes (whether RO is used to demineralise the feed water, or not). Sometime RO can help, however, microbial control does not necessarily require RO.

In cases where microbial control is required, but demineralised water is not, is RO always the best solution?

Is RO required for endoscope reprocessing?

This leaves open the question as to whether RO is required in endoscope reprocessing.

Many endoscopy departments around Australia are already meeting the Table 7.3 water quality requirements without RO. If the water quality is meeting the requirements of the Standard without RO, would the addition of RO bring any significant benefits equivalent to or greater than the associated additional costs?

On the other hand, is there any reason to avoid RO? RO in this context produces a particular water type: demineralised water. Two characteristics of this water type can be:

  • Corrosivity: Very low dissolved solids, no alkalinity → very low buffering potential → variable (often low-ish) pH → water that can corrode and dissolve some metals which are common in water contact systems, such as copper and brass.
  • No chlorine Chlorine is in our drinking water to control microbial activity. The water treatment process removes the chlorine (i.e. removes the chemical which was controlling microbial growth in the feed water).

Demineralised water cannot be safely used in most existing Endoscopy Departments, because of a range of issues related to compatibility, corrosion, conductivity or risk of microbial growth.

Using RO to demineralise water for endoscope reprocessing would mean changing all of the above, or designing and fitting out a new Endoscopy Department Cleaning Room to suit. This can be more involved—and more expensive—than it might first seem.

Consequences of incorrect use

Already in Australia, some have tried and failed. You may have heard of some of the mistakes made by others, maybe even in your own hospital or clinic: Mistakes including (but not limited to) misunderstanding the complexity of heating demineralised water to 35°C ±2°C and/or 44°C ±2°C (for example), with different materials compatibility challenges and control requirements.

Poor outcomes in this area that we have heard of, resulting from poorly conceived solutions installed by some others, have included:

  • Failures in heating and plumbing systems, leading to disruption and sometimes water damage in the surrounding area.
  • Extended AER cycle times, e.g. AER stops or faults while waiting for the water treatment system to get the temperature right – slowing down reprocessing and creating additional operational costs in the clinic such as extra staff hours/employment costs.
  • Explosions in microbial growth in the feed water supply due to poor hydraulic and/or system design exacerbated by the (warm) temperatures of the feed water.
  • Cancelled surgeries/procedures due to problems with endoscope reprocessing as a result of the above failures.

These sorts of mistakes ultimately must be rectified, usually at additional cost to the HSO – sometimes a ‘budget’ or poorly conceived solution can end up being very expensive indeed.

It is possible to overcome the challenges of using demineralised water in endoscope reprocessing. However, to do so reliably does not require ‘just’ an RO and some stainless-steel pipe. The water temperature requirements and microbial control aspects add a significant degree of complexity to the required solution if using demineralised water. This all translates to increased capital expenditure.

Some feed water sources (e.g. with very high chloride levels) may need a complex water treatment plant including RO and new plumbing. However, in other cases, the existing arrangement in many Endoscopy Departments, with microfiltration, and sometimes other microbial control processes, may be sufficient to meet the requirements of the Australian Standard. If a demineralised water system is not required at your site to comply with the Standard, then perhaps the best solution is a simpler water treatment system, that does not require new plumbing and other major expenditure.

The main argument against ‘RO’ then, if it is not required, is cost – both capital costs and the ongoing operational costs of a more complex system, or the additional costs which can be associated with installing a ‘budget’ RO system that creates further problems down the track, such as potential system and equipment failures, increased microbial challenge, additional (otherwise unnecessary) maintenance costs, and/or extended AER cycle times leading to other hospital costs in additional staff hours or cancelled surgeries.

Other options

There are cases where RO may not be required, but other water treatment processes may be beneficial: Water Softening, additional filtration, UV disinfection, chemical dosing, or automated hot water disinfection, are examples of some different options which may be suitable. The best fit will depend on the local feed water quality and other site-specific requirements. There can be many variables from site to site. At the end of the day, the goal is to reliably meet the AS4187 Standard, and the solution should be tailored to site-specific challenges and requirements: including incoming water quality, spatial limitations, number of AERs, types of cycle required, and usage/duty hours.

“Can we use our CSSD RO?”

In most parts of Australia, a sophisticated water treatment plant including RO producing demineralised water is absolutely required for CSSD to meet the requirements of the Standard in that department. However, CSSD is different from Endoscopy. The requirements are different.

It might be possible to take a feed to Endoscopy from the CSSD demineralised water loop, however, it also may not be possible or advisable, too. There can be additional unanticipated challenges in taking water from a water treatment plant intended for one purpose (CSSD) and attempting to use it for a different purpose, such as endoscope reprocessing.

For example: Remember the different water temperature requirements in each of the two different departments? CSSD uses water at a different temperature from the Endoscopy Department. Modifying the CSSD’s treated water supply temperature to suit the Endoscopy Department still brings the challenges described above and would add further cost and complexity to make the system suitable for the two different purposes, compared to having a separate water system for each department. It could require additional heating or cooling of the CSSD’s treated water, and/or management of “dead-legs” and microbial control, and/or extending the AER cycle times to allow for changes in temperature whenever water is used in CSSD – all challenges possibly leading to unnecessary extra costs.

The amount of water used in endoscope reprocessing is different too. Adding a medium-sized Endoscopy Department to the CSSD’s demineralised water loop could double the size – and cost – of the required ‘combined’ water treatment plant.

If it’s not necessary, are the additional costs and complexity of trying to use one water treatment system for two different purposes a good return on investment? Or would the challenges, risks and costs be better managed with different water treatment systems for the different needs in each different department?

To RO, or not to RO? That is the question.

Aquacure has been installing water treatment systems, including RO machines for both CSSD or Endoscopy, in Australia for over 33 years. And yet, our advice very often is that RO may not be required for endoscope reprocessing.

There are times when RO should perhaps be avoided: especially when the choice may be between a simpler system (without RO) which is meeting the requirements of the Standard, and a poorly conceived or ‘budget’ generic RO system which may not be appropriate for a particular site or situation and could create maintenance complications and costs rather than the improvements desired.

To RO, or not to RO? That is the question. RO might be required at your HSO, or it might not. If it is required, then the overall best solution may be completely different from at another site. If it isn’t required, there may be something else which could be better – and more cost effective – for you. At the end of the day, for the answer to this and other water treatment related questions, the individual requirements of each site must be considered.

A suitably experienced water treatment specialist, such as Aquacure, should be engaged to provide the best, site-specific solution, based on achieving the best long-term performance in the clinic and reliable compliance with the Standard. An unnecessary solution, or a poor-quality solution that ultimately creates further problems and costs, while the right solution will also be the best value solution in the long run. Our paper on selecting the right solution can be downloaded here.

If the right solution is not RO, then it shouldn’t be RO. Getting it right the first time, RO or not RO, will save a lot of future heartache – and a lot of money.


Christopher Hall



[1] AS/NZS 4187:2014, Clause 5.6.6
[2] AS/NZS 4187:2014 (Amd2:2019), Clause
[3] A fully automatic, brine regenerated cation exchange ‘Water Softener’. These are widely available.
[4] AS/NZS 4187:2014 (Amd2:2019), Section 7
[5] Cantel Australia (Medivator), In Vitro Technologies (Steelco), and Device Technologies (Reliance)