March 20, 2024

CSSD RO site installation – design considerations

Ensuring that the water produced by CSSD ROs complies with the current healthcare standards and ensuring that hospitals and clinics have a reliable source of water for their sterilisation departments is not as simple as designing an isolated water treatment system. There are additional site specific factors that require consideration during the design phase which centre around the installation site and the planned operation of the CSSD RO.


Most municipal based CSSD ROs will be fed with local tap water which has already been filtered, demineralised and sanitised. To produce CSSD compliant water from tap water, the sanitiser and any remaining minerals will need to be removed, but as the suspended solids have already been removed by the previous water treatment process, additional filtration is not required for CSSD ROs when tap water is the feed.

Other common types of feedwater used to produce sterile water for hospitals and health clinics, particularly in remote locations which don’t have a reliable source of potable water, include groundwater and seawater. Groundwater has the advantage that it is usually has a low suspended solids concentration and lower salinity than seawater. As there is no sanitiser present in groundwater, the pre-treatment system will be different from that installed for tap water. Seawater will again require a different treatment system as higher salt levels in the feedwater will require tighter membrane pores in the reverse osmosis process as well as intake screens and chemical dosing systems which will need to be carefully designed to ensure the membranes are not fouled.


Waste streams

All RO plants produce a waste stream in addition to a permeate stream. The higher the recovery of the RO system, the lower volume but higher salinity this stream will be. A two pass RO, which treats the permeate twice, will produce two waste streams (one from each pass) but the waste stream from the second pass usually has low enough salinity that it can be recycled back to the feed. The waste streams for a CSSD RO will also need to be carefully considered during the design process as in addition to the standard waste streams from a Reverse Osmosis system, there is the added waste streams from the sterile water storage tanks which are dumped whenever there is an indication of contamination.

Consideration also needs to be given during the design phase about where these waste streams will end up and if the receiving environments can accept this quality and volume of waste water. Seawater desalination systems will need to be run low recovery and with minimal chemical addition so the waste stream can remix back into the ocean without adversely effecting the marine environment. The reject stream from high recovery groundwater systems will usually have a high concentration of total dissolved solids so care must be taken when considering where these streams will be disposed of.


CSSD RO installation locations commonly have a lack of space. With the updated timeline of AS4187 compliance, hospitals and clinics are often unable to take the time (or expense) required to construct new plant rooms to house an expanded and updated water treatment system. Instead most healthcare campuses are having to make use of whatever space they currently have available. Existing indoor space is generally quite cramped as it will have been used for other purposes in the past and space is at a premium in hospitals and health care centres.

CSSD ROs consist of extensive equipment: pre-treatment filters, membrane vessels (consisting of single or double pass), polishing components, sterilisation systems and distribution tanks and pipework. The larger the volume of treated water required, the larger the space requirement. During design, the required equipment must be matched to the available space. This can often lead to a redesign, either through the selection of smaller membrane vessels, a change in the overall recovery rate of the water treatment system or a change in the type of feedwater used.

If internal space is found to be too limited, some hospitals are opting for exterior installation through the construction of prefabricated rudimentary outdoor enclosures which can shield the treatment units from the elements. Housing the CSSD ROs outside does have the advantage of there often being more space available and access for servicing can be easier. However, exterior installation has the disadvantage of having the water treatment system exterior to the hospital (and therefore the central sterilisation supply department) which can require extensive distribution networks to pump the water into the hospital. Additionally, an exterior location can require the installation of a power source where previously there may not have been this facility.


Given the high power requirements for reverse osmosis based treatment systems, careful thought needs to be given to how the power to run the CSSD RO will be sourced and provided at the installation site. It can be helpful to ask a range of questions which can aid in the development of the electrical system which will power the water treatment system.

  • Is there an existing three phase outlet at the installation location?
  • Is only single-phase power available onsite?
  • Is there a limit to the current available onsite?
  • Is there renewable energy available, if not, is this an option?
  • If the unit is outside, is there power available at the proposed installation location or does it need to be wired in?

Servicing requirements

Given the complexity of CSSD ROs, it is inevitable that at some point they will fail if they are not maintained. As the treated water is required to sterilise medical instruments, it is important to have service contracts which include preventative maintenance in place prior to operation as servicing companies may be unable to attend site on short notice – creating unnecessary and costly downtimes.

Moerk Water have extensive experience installing CSSD ROs at different locations and designing bespoke systems for each site which take many of these factors into account. Contact Moerk Water to ensure your CSSD RO is appropriately designed for your location.