Using temperature control

The primary method used to control the risk from Legionella is water temperature control. Water services should be operated at temperatures that prevent Legionella growth:

Hot water storage cylinders (calorifiers) should store water at 60°C or higher
Hot water should be distributed at 50°C or higher (thermostatic mixer valves need to be fitted as close as possible to outlets, where a scald risk is identified).
Cold water should be stored and distributed below 20°C.

We can routinely check, inspect and clean the system, in accordance with the risk assessment.

We will identify ‘sentinel’ outlets (furthest and closest to each tank or cylinder) for monthly checking of the distribution temperatures.
We will also check the hot water storage cylinder temperatures every month and cold water tank temperatures at least every six months.

Stagnant water favours Legionella growth. To reduce the risk we can remove dead legs/dead ends in pipe-work, flush out infrequently used outlets (including showerheads and taps) and clean and de-scale shower heads and hoses at least quarterly.

We will also clean cold-water storage tanks and drain water from the hot water cylinders to check for debris or signs of corrosion.

We can design systems to minimise Legionella growth, by:

keeping pipe work as short and direct as possible;
adequately insulating pipes and tanks;
using materials that do not encourage the growth of Legionella;
preventing contamination, eg by fitting tanks with lids and insect screens.

Additional controls

We can analyse water samples for Legionella periodically to demonstrate that bacteria counts are acceptable. The frequency should be determined by level of risk, in accordance with the risk assessment.

Other control methods

Other methods to control Legionella include copper and silver ionisation and biocide treatments (eg chlorine dioxide). To ensure that they remain effective their application will need suitable assessment as part of the overall water treatment programme including proper installation, maintenance and monitoring.