Sterilising new domestic installations and suspected contaminated.

Water Treatment and Air Services

Process and Procedure

It is recommended that all new domestic installations such as cold water storage tanks and the hot and cold services, incoming mains and the outlets be sterilised before being put into use, in accordance with the Health and Safety Executive recommendation BS8558:2015/ACOPL8.


The standard procedure requires a 1 hour contact time of 50ppm free residual chlorine concentration. The process is repeated if this level falls below 30ppm after the 1 hour contact time.

Other Situations Requiring Sterilisation:

  • Where extensions or alterations have been carried out
  • Where it is suspected that contamination has occurred
  • Where a system has not been in regular use, or regularly flushed


It is a requirement that samples for Bacteriological and in some cases Legionella, are taken on completion of the sterilisation. The number of samples taken should represent the system as a whole, normally determined as 10% of the total number of outlets.

Provided there is no suspicion that the system has been fouled prior to sterilisation, the system may be put into service before the sample results are published.

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Unit 5, Byfleet Technical Centre,
Canada Road,
KT14 7JX

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