WATER SAFETY PROCEDURES


Flushing of healthcare water systems – a ‘necessary evil’?


‘Flushing water systems could save lives, waste money, cause fatalities, or be illegal’. By the time one has resorted to flushing it may be at worst ‘failure’, or, at best, ‘a necessary evil’. The presence of Legionella in a water system is not a fluke, and its root cause is not lack of flushing. Flushing is a means not an end. So says Dr Nick Hill, Authorising Engineer (Water) at Water Quality London, and the former Chair of the IHEEM Water Technical Platform. Here he sets out the purpose, methods, benefits, shortcomings, and pitfalls, of flushing outlets such as taps and showers as part of the control process for Legionella in healthcare water systems.


Why do we flush taps, showers, and other parts of water systems? Generally, there are two circumstances which involve flushing of water: n As part of a new-build or refurbishment project, where flushing follows initial filling of a water system, and is designed to remove any contamination from the manufacturing, installation, and disinfection processes, and to keep the water ‘fresh’ until the building is handed over, often accompanied by continuous biocide dosing.


n As a routine operational practice.


This paper focuses on the latter circumstance. The reason for flushing water from parts of a system is to remove stagnant water because it contains, or it is suspected of containing, legionellae. All stagnant water in the water systems of buildings should be considered as potentially contaminated with legionellae. There are many people who believe that flushing is a method of temperature control, indeed almost a necessity to maintain cold water at a temperature below 20˚C, and to compensate for hot water system deficiencies to bring water at 55˚C to each outlet. Unfortunately, flushing is not an effective method of controlling water temperature.


Proposed water system design Recently, I have been presented with a proposed water system design for a new hospital which included an automatic flushing system for maintaining cold water temperature below 20˚C. It was suggested that the system would monitor cold water temperature, and when it reached 20˚C would open solenoid valves at sentinel locations, to flush away the water until the temperature reduced to below 20˚C. My response to this was to state that such a system would be both illegal and ineffective. It would be ineffective because the proposed hospital is in London, where the temperature of


56 Health Estate Journal November 2020


water supplied by the water undertaker (the water utility organisation which provides the public water supply) typically reaches 20˚C during the summer/autumn seasons. Therefore, flushing water out of the building’s water pipework would only introduce more water at 20˚C or above. The system would be illegal because it would be continually running water to waste during the warmer months, and waste of water is prohibited under the Water Supply (Water Fittings) Regulations.1


It is also a waste of money. An advisory role


As an IHEEM Registered Authorising Engineer (Water), I can ‘take the horse to water, but I cannot make it drink’; in other words my role is not to ‘authorise’ or ‘derogate’, but rather to provide advice as to whether or not such designs meet the requirement that risk elimination/control should meet the standard of ALARP (as low as reasonably practicable). I have described the role of the AE (W) in a previous HEJ paper.2


However, the


designer of the water system for this new hospital has since revised its design in three ways: n The critical control criteria are now based on the ‘+2˚C + 2˚C’ described in HTM 04, Part A,3


temperature should be no greater than


Identifying infrequently used outlets HTM 04 (2016) Part B,5


para. 6.24, includes i.e. the cold water tank


in a typical list of issues to be considered in a risk assessment, ‘infrequently used outlets’, but does not indicate how they are known to the risk assessor. Para. 6.80, under the heading ‘As-fitted drawings’, states that “...drawings will be necessary to perform the temperature control checks on the systems and will assist in identifying any potential problems with poor hot water circulation and cold water dead-legs where flow to infrequently used outlets can be low”. This implies that cold water temperatures should be appraised, presumably by the Authorised Person (Water), to determine if they indicate stagnation due to infrequently used outlets. Personally, I think this would be quite difficult or impossible. Running the


While this refinement of the design is more palatable than the original proposal, it indicates fundamental failures, namely to design for elimination of risk rather than control, to base design on risk assessment, and to do so the earliest stage of a project as required by HTM 04 Part A.3


Bearing in


mind that I demonstrated that large hospitals can achieve the ‘+2˚C + 2˚C’ criteria even during a heatwave,4


in


buildings ranging in age from 1970s to 2010s, without automatic flushing systems, why in the proposed new hospital would one think that such criteria cannot be met?


2˚C above the temperature at the incoming water meter, and the tap temperature should be not greater than 2˚C higher than the tank temperature.


n If these critical control criteria were not met, the system would alarm first, then start flushing after a pre-determined period, to allow time for the maintenance team to respond. The designer’s original proposal was for the system to flush first, then alarm.


n The period of flushing would be time limited rather than indefinite.


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