Design considerations for Central Decontamination water supply

With an increasing focus on infection control in hospitals and healthcare facilities, ensuring the quality of the disinfection system is maintained at every stage is crucial. A key part of this is ensuring a reliable source of purified water in line with the Health Technical Memoranda (HTM) guidance.

The Health Technical Memoranda (HTM) provides detailed guidance on the design, installation and operation of healthcare facilities. This includes the design of the buildings, such as acoustics and fire safety as well as the building systems such as medical gas supplies, heating, ventilation and water. The memoranda also includes documents on the design and required standards for decontamination of surgical instruments and endoscopes. In addition, ISO 15883 specifies the general performance requirements for Washer Disinfectors and the quality of water supplied to them.

In the majority of healthcare facilities, endoscopes and other instruments that cannot be thermally sterilised at temperatures above 60C are chemically disinfected and rinsed in purified water using Automated Endoscope Reprocessors (AER) or Washer Disinfectors (WD). There are a range of factors to consider when specifying the system that supplies the purified water.

The first is to consider the method of purification. One of the most cost-effective technologies is reverse osmosis (RO). This uses a semi-permeable membrane to separate and remove 99% or more of the dissolved solids, particles, colloids, organics, bacteria and pyrogens from the water. The feed water enters the membrane under pressure and the water molecules pass through, while the contaminants are captured and discharged. The main benefits of RO systems are that they do not require the addition of hazardous or expensive chemicals and as the only ongoing expense is electricity, the cost of producing the water is low.

Veolia Water Technologies has a number of RO solutions including the compact heat-sanitisable Thermapure™ and OSIRIS, a fully integrated, packaged reverse osmosis water treatment system that features automated self-disinfection.

Once the method has been selected, the next step is to establish the requirements for the system, this includes:

Quality of water required

This is dictated by the type of equipment being sterilised, and as such the corresponding HTM document – either HTM 01-01 (Decontamination of surgical instruments) or HTM 01-06 (Management and decontamination of flexible endoscopes) provides the required parameters.

The AERs or WDs to be fed

The number and type of units that the system will supply must be established at an early stage. This includes details of the peak volume of water per cycle, the number of cycles per hour and peak draw rate for each unit. This will vary significantly between different manufacturers’ products, as will the layout and type of connections to the supply pipework.

Required performance of the RO

Is there a level of operation that the system must maintain? For example, the number of
hours per day it will be operating for and the level of up-time it must meet. Will you require N+1 design or similar? For example, a duplex RO plant or twin ring pumps to achieve close to a 99% up-time.

Capacity flexibility

Does the system need to include additional capacity or the option for simple expansion to meet future needs?


Who will be carrying out the scheduled maintenance checks and servicing? Will an in-house team be responsible, or will a water treatment specialist be contracted?

Quality of the incoming mains water

The quality of the water supply to the RO unit should be monitored and tracked, preferably over the previous 6 to 12 months, so that the correct system can be selected and installed.

Depending on the quality of the water, pre-treatment measures may be required. In hard water areas, a water softener should be installed to improve the performance of the RO system and remove a potential food source for any bacteria. Carbon filtration should also be considered where there are high levels of free chlorine to ensure the longevity of the RO membrane.

Furthermore, once the system is installed and in operation it is important to ensure that the water quality is tested regularly and in line with HTM guidance. Final rinse water quality tests (at the point of use) should be carried out weekly to ensure it meets the parameters set by HTM. The results of the microbiological (total viable count) test should be recorded and plotted to identify trends in the findings and to isolate unusual results. While there is no requirement for weekly or monthly testing of the quality of the water from the RO outlet, a quarterly test is recommended as best practice to validate the final rinse water quality results. The HTM also recommends that a full test and analysis of every part of the system is carried out yearly.

Veolia Water Technologies can provide help and assistance in selecting, installing and commissioning the right system for each facility.

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Kalpesh Shah

About the Author

Kalpesh Shah

Kalpesh Shah is the Industrial Sales Manager for Veolia Water Technologies UK. He started out working within internal sales in the early 90's before moving into international sales. In 2000, his focus led him into project management where he worked on a variety of complex and demanding projects with clients ranging from the NHS, Industrial and Pharmaceutical, for over a decade. He then moved into pharmaceutical business development which he did successfully until his promotion to Industrial Sales Manager. Kalpesh has 26 years of extensive experience with all types of industrial water treatment systems and processes. He is able to support his clients with the design and implementation of efficient water treatment systems using an array of technologies.