The frequency of cleaning and disinfection for cooling water systems is described as “If a system can be shown to be free of fouling, i.e. the deposition of particulate material and debris, there is no need for it to be cleaned at a set time interval, rather the system should be cleaned whenever it is known or suspected to have become fouled. However, as cleaning operations are disruptive, it is common to adopt a precautionary approach, with cleaning operations being scheduled to coincide with planned shutdowns or at a predetermined interval, e.g. six monthly” which for the majority of sites would be a predetermined interval such as six monthly.
For hot and cold water systems ACoP L8 says that they should be cleaned and disinfected in the following situations:
(a) If routine inspection shows it to be necessary
(b) If the system or part of it has been substantially altered or entered for maintenance purposes in a manner which may lead to contamination; or
(c) During or following an outbreak or suspected outbreak of legionellosis.