Modern hospitals rely heavily on the support of sterile services departments (SSDs) to ensure that equipment is cleaned and sterilised to consistently high standards. To achieve this, SSDs require large volumes of high purity water for a range of uses, from endoscope and equipment washing and sterilisation, rinse water for automated washer disinfectors, and for use in autoclaves. In addition, high purity water is used both to act as a final rinsing agent to remove any remaining traces of dirt, detergent or chemicals from washer-disinfectors and to provide steam for thermal disinfection and steam sterilisation.

The standards governing the use of purified feed-water are defined in (S)HTM 2030/2031, which provides guidelines for washer disinfectors and the quality of feed-water for steam generators. In particular, (S)HTM 2030/2031 lays down recommended limits for a number of key operating parameters including electrical conductivity, total dissolved solids (TDS) and water hardness, plus the acceptable concentrations of Chlorides, heavy metals, Iron, Phosphate and Silicate and the maximum levels of bacterial endotoxin and total viable count.

The critical nature of the work carried out by SSDs means that adherence to standards such as (S)HTM 2030/2031 is essential and, just as importantly, that the equipment used is correctly designed, manufactured and validated. In particular, feed-water has to be carefully treated or purified to ensure that it does not introduce contaminants into subsequent stages of the cleaning and sterilisation process.

One of the most effective methods of providing a supply of high purity water to meet the (S)HTM guidelines is reverse osmosis (RO), where mains water is fed under pressure into a module containing a semi-permeable membrane. The membrane removes a high proportion of impurities, including up to 98% of inorganic ions, together with virtually all colloids, micro-organisms, endotoxins and macromolecules, with the efficiency of the process being such that up to 75% of the feed-water passes through the membrane, forming a purified permeate, with impurities being removed in a residual concentrate stream which is run to drain.

RO systems generally include a pre-treatment package that is specifically designed to meet the characteristics of the feed-water. Typically, this additional equipment would include a base-exchange softener to remove hardness that could otherwise scale downstream membranes and, where necessary, to provide a flow of softened water directly to the washer-disinfectors. Further protection of the RO membranes is provided by passing the water through activated carbon filters, to remove free Chlorine and organic contaminants, with any remaining fine particulates being removed by a fine filter before the pre-treated water enters the RO plant.

The latest developments in water purification technology mean that many systems require relatively little space for installation. Systems are generally designed with full redundancy ensuring that the washer disinfectors and clean steam generators receive an uninterrupted supply of purified water, even in the event of one unit failing to operate or being taken out of service for maintenance.

Similarly, containerised and self-contained RO purification units that can be located outside the hospital buildings are also now available to enable SSDs to maximise the space available. These systems have been developed so that they can be installed quickly and simply, with a minimum of disruption to hospital schedules; once in place these systems normally have low operating costs, requiring minimal maintenance or user intervention.

Finally, with an increasing number of SSDs operating 24/7, the advances in water purification technology to meet (S)HTM 2030/2031 standards mean that it is now possible to provide a secure, efficient and reliable water purification solution even in the most demanding of environments.