Sterile services / Decontamination

Water purification for sterile services, decontamination and endoscope reprocessing

High quality purified water is critical for use with washer disinfectors, automated endoscope reprocessors (AERs) autoclaves and steam sterilisation systems, for cleaning and decontaminating endoscopes and other hospital instruments.

In each case, raw source water, normally drawn from mains supplies, must be purified to meet the requirements of the latest HTM guidelines. These include:

HTM 01-01 part a.

This covers the requirements for the use of high temperature steam sterilisation and porous-load sterilisers. Steam can be generated by a central boiler system or a stand-alone steam generator; in each case, feedwater has to be correctly treated to ensure that contaminants are not carried over into the steriliser.

HTM 01-01 part b.

This covers the requirements for using washer-disinfectors, and specifies the required water quality for criteria such as hardness, temperature, ionic contaminants, – heavy metals, halides, phosphates and silicates – microbial population and bacterial endotoxins. Depending on the type of washer-disinfector, purified water can be used for process washing and thermal disinfection, as well as for the final rinse.

HTM 01-06 part c and part e.

Part a covers the operation of washer-disinfectors, with reference to the supply of purified water for process and final rinse water. Part e covers the testing regime and specifies the permitted maximum level of measurements such as acidity (pH), electrical conductivity, hardness and total viable count (TVC) of micro-organisms.

Depending on the application, water purification is normally achieved using either a reverse osmosis (RO) or deionisation (DI) system.

Water purification technologies

Reverse osmosis is a proven and highly effective method of removing inorganic ions and larger, non-ionic contaminants from raw water streams. An RO system operates by passing pressurised feedwater through a specialised semi-permeable membrane, which is capable of rejecting up to 98% of the mineral salts, silica and organic compounds and over 99% of bacteria that may be present, and produces a stream of purified water known as the permeate. A waste or concentrate stream containing the rejected impurities is also produced that can often be recycled.

By comparison, deionisation technology removes ions and charged particles either using electric fields or through ion exchange in resin beds. Although deionisation can produce a higher purity of water than RO, the latter is more than adequate to meet the needs of sterile services and decontamination services, as defined by the HTM guidelines.

From a practical perspective it should also be noted that,  

  • RO is cheaper to install and operate than DI;  
  • RO removes particulate matter, organic molecules and pyrogens that cannot be eliminated using DI 
  • RO water is less corrosive to steel and copper pipework and storage vessels than DI water 
  • RO systems are simpler and less expensive to maintain that DI plant. 
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