FEATURE
fixtures and installing trace heating on hot water return legs where lower temperatures may occur. Cooling tower installations used in heating and ventilation systems require separate and special consideration.
The source of P. aeruginosa is less certain, since the bacteria can enter water systems via outlets within the building, like taps and shower heads, and colonise the pipework close to these fittings. As the water temperatures necessary to prevent bacterial growth in hot water distribution systems can present a risk of scalding to vulnerable users, it is recommended practice to install thermostatic mixing valves at, or close to, the outlet to control the final temperature of water at the outlet. The design and location of these devices can, however, increase the risk of colonisation by P. aeruginosa, which may increase the need for monitoring and routine maintenance.
Risk Management is Crucial Healthcare establishments are required by law to conduct an assessment of the health risks associated with water supply systems. The duty holder must appoint a competent person, or persons, to conduct such an assessment; take responsibility for
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managing an appropriate risk control scheme and keep detailed records. The risk assessment should include a clear allocation of management responsibilities, evidence of the competence and training of key personnel, a description of the water system and procedures for the operation, monitoring, inspection and maintenance of the system. The risk assessment should be updated regularly, especially when changes to the design or use of the system mean the original assessment may no longer be valid.
On-going risk management should include regular sampling of water at all outlets within a facility. For P. aeruginosa, the guidance advises testing at six-month intervals. Testing should take place at times of low or no use of the outlet in question, since water flow can quickly wash away bacteria escaping from the biofilm in pipework close to the outlet. If bacteria are detected, re-testing both before and after flushing the outlet is advised to determine whether the problem is in the local pipework or the wider water supply system.
Tackling Infected Areas Where P. aeruginosa contamination is detected, the outlet concerned should be taken out of service,
but regularly flushed to prevent stagnation. Remediation actions include the removal of items like flow straighteners, or flexible connectors that can provide a habitat for bacterial growth, together with measures to reduce the splashing that can lead to contamination of outlets in use. The installation of point of use filters can be used as a short-term mitigation strategy to provide contaminant-free water, but such filters must be maintained and replaced in accordance with manufacturers’ instructions.
In some circumstances it may be necessary to carry out a disinfection of the water supply system. Modern high performance biocides, like the Ultralox 40 active chlorine solution from SUEZ, have been shown to give very effective results against both legionella and Pseudomonas aeruginosa, combined with a low hazard classification and good environmental profile. The availability of automated dosing systems and reliable monitoring and control simplifies the uses of such systems, both for initial disinfection and for continued low-level use to prevent further bacterial growth.
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