20 August 2015 - Category: AS NZS 4187 Standard

Water for Disinfection in AS4187: Where do I start, what do I need and why?

By Chris Pezet

Since the 2014 release of the AS/NZS4187 we have had a large increase in customer enquiries regarding water for use in disinfection. A common misconception is that “to comply I simply need a Reverse osmosis system.” The answer to this is NOOOooooo not quite, if it were only so simple that would be great, but it isn’t, so read on.

Table 7.2, declares a particular water quality you are required to comply to, this table requires technology to create water to that quality, plus technology to maintain stored water to retain the quality.

What are the differences between create and maintain?

Create: Generally will require Reverse Osmosis system (RO) sized correctly delivering water into a storage tank. (This will remove 95-99% of dissolved contaminants and bacteria if engineered correctly)

Storage: It is uneconomical due to substantial capital costs to have an RO unit for direct flow into a washer, so you will need a storage tank.

Storage issues: Mains water from your municipal supply has residual control for micro-organisms and pathogens, ie: Chlorine dosing, so bacteria is of lower concern when using your tap water. With stored RO water you have in the purification process removed all the residual micro biological control chemicals so your tank of RO water has no process to prevent bacteria breeding potentially out of control. This leads to endotoxins which creates an issue for patients if present on theatre instrumentation. 

The requirement for micro-organism level is stated in table 7.2 on the last 2 lines, ECU and EU (micro and endotoxin levels)

Maintain (1): how do I maintain my stored water to the purity level required? You have a couple of choices.
a)    Store at greater than 65^oC, this prevents micro-organisms proliferating.
b)    Have a continuous recirculating ring main from storage tank to washers and sterilizers and back to the tank.

On the ring main utilize ultraviolet light for continuous bacteria address (99.99% kill rate). Also on the ring main use cartridge ultrafilters (<0.1um) installed after the UV to catch any endotoxins that may be present, again continuous address via the recirculation system.

Maintain (2): Any storage system of pure water requires periodic disinfection itself. This needs to be part of your own SOP’s and can be achieved via either:

-    Chemical disinfection
-    Heat disinfection
Either is possible but both have pro’s and con’s depending on your site that need to be considered.

Other Considerations for your pure water treatment system that we do not have time to go into in this tech sheet include:
Materials of construction, system disinfection times and return to service rates, correct flow and sizing of recirculation systems, instantaneous demand versus daily requirements, differences between high grade water systems and residential systems, differences between Table 7.2 (disinfection) and EN285 steam sterilizer water and steam requirements, care and pre-treatment for RO systems, sampling techniques and sampling devices. These all need to be considered when designing a system to ensure minimum hassles for the CSSD to create and keep your disinfection  and autoclave water at the correct purity.

Any questions can be answered by contacting Gallay Medical and Scientific (1300 425 529) and asking for your local Medical Product representative. To find out more about Gallay's new range of Reverse Osmosis Water Systems, please click here.