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Table 1: Recommended actions following legionella monitoring in a cooling tower
Legionella concentration Colony forming units per litre of water	Action required
100 or less	none, system is satisfactory
More than 100 but less than 1000	either: a resample, if similar count repeated review control measures and risk assessment to identify remedial action b if majority are similar then immediately review the control measures and consider disinfection
More than 1000	resample and immediately review control measures and risk analysis to identify remedial action, including possible disinfection of system

Table 2: Recommended monitoring (M), inspection (I) and servicing (S) frequencies for hot and cold water services.
System/Service	Task	Frequency
Hot water services	Arrange for samples to be taken from hot water calorifiers, in order to note condition of drain water	Annually	M
	Check flow and return temperatures at calorifiers, plus temperature of drain water	Monthly	M
	Check water temperature after 1 minute at the sentinel taps to see if it has reached 50°C	Monthly	M
	Visual checks of internal surfaces of calorifiers for scale and sludge.	Annually	I
	Check representative taps for temperature as above on a rotational basis	Annually	M
Cold water services	Check tank water temperature remote from ball-valve and mains temperature at ball-valve. Note maximum temperatures recorded by fixed max/min thermometers, where fitted.	Summer and winter	M
	Check that water temperature is below 20°C at the sentinel taps after running the water for 2 minutes	Monthly	M
	Visually inspect cold water storage cisterns and carry out remedial work where necessary. Check representative taps for temperature as above on a rotational basis	Annually	M
Shower heads	Dismantle, clean and descale shower heads and hoses	Quarterly or as necessary	S
Little-used outlets	Flush little-used outlets	Weekly	S