Legionella bacteria can be present in drinking water facilities. Compliance with applicable water quality standards is required.


Legionella bacteria can cause an infection known as Legionnaire’s disease, and although rare, can lead to a form of pneumonia. There is also a milder form of infection, known as Legionella flu. Legionella was first identified in 1976 after an epidemic outbreak of pneumonia among American Legion conventioneers.

The bacterium that causes the disease is found in the ground and in tap water in very small concentrations. The concentration is so low that the bacteria are not normally a health risk. It is only when the Legionella bacteria concentration increases that it becomes a problem. This increased concentration occurs in water at temperatures between 25 ºC (77 ºF) and 55º C (131 ºF). In these situations, large colonies are formed when the water remains stagnant for a long period of time. Infection is via the lungs when contaminated droplets of water are inhaled. The time between infection and the first symptoms is somewhere between 2 and 10 days. The first symptoms are rapid onset of headache, muscle ache, and a general feeling of malaise, followed by pneumonia and a fever over 39 ºC (54 ºF).The patient starts to cough and sometimes experiences shortness of breath. A number of patients experience vomiting and diarrhoea. The disease can have serious consequences, but can be properly treated by immediate administration of suitable antibiotics.

In field execution, there are 2 situations that can pose a health risk

  • Showers (in temporary facilities)
  • Cooling towers

Preventive and Protective Measures

The following preventive measures can be taken for domestic water systems

  • Hot and cold water systems should be designed to aid safe operation by preventing or controlling conditions that permit the growth of Legionella and allow easy cleaning and disinfection.
  • Materials such as natural rubber, hemp, linseed oil‐based joining compounds and fiber washers should not be used in domestic water systems.
  • Materials and fittings used in water systems should be known not to support microbial growth.
  • Water storage tanks should be fitted with covers that comply with the national water regulations, and insect screens fitted to any pipe work open to the atmosphere (such as the overflow pipe and vent).
  • Multiple linked storage tanks should be avoided because of operational difficulties due to possible unequal flow rates and possible stagnation.
  • Accumulator vessels on pressure‐boosted hot and cold‐water services should be fitted with diaphragms that are accessible for cleaning.
  • The point of use for hot water generators, with minimal or no storage for remote low‐use outlets, should be considered.
  • Thermostatic mixing valves (TMV), if any are fitted, should be sited as close as possible to the point of use; ideally, a single TMV should not serve multiple

tap outlets but, if they are used, the mixed water pipe should be kept as short as possible.

  • Where a single TMV serves multiple showerheads, it is important to confirm that these showers are flushed frequently.
  • The storage capacity and recovery rate of the water heater should be selected to meet the normal daily fluctuations in hot water use without any drop in the supply temperature. The minimum water delivery temperature should be set at 60 °C (140 ° F).
  • The hot water circulating loop should be designed ideally to give a return temperature to the storage water heater of 55 °C (131 °F).
  • Hot water distribution pipes should be insulated sufficiently to not affect cold water pipes.
  • Cold‐water storage must be thermally insulated to prevent excessive temperature increases.

The commissioning of a cooling unit can pose a health hazard. A cooling system may consist of a cooling tower, evaporative condenser or other cooling element, the recirculating pipe work, the heat exchanger, pumps, and ancillary items such as supply tanks and pre‐treatment equipment. All of these items should be subject to appropriate management and control systems. Operation manuals should be available for each water system and contain the following

  • Dosing methods (automatic or manually); if automatic, the means of confirming operations
  • Recording of quantity and frequency of chemical application
  • Results of monitoring and any actions conducted
  • Normal control parameters
  • Limits, with corrective actions, for out‐of‐specification situations or where plant operating conditions or makeup water quality have changed
  • Cleaning and disinfection procedures



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