The Legionella bacterium likes water temperature in the 37º region (ie blood temperature).
Most bacteria are killed off at 50º but Legionella can go on to 55º. It follows, therefore, that you need to keep stored hot water at 60º to be safe.
Stored water in roof tanks can get hotter than desirable in the summer which is why cold water tanks in roofs are (should be) lagged.
The water in roof tanks will not get all that warm but you need to know, without having to take temperatures.
It is now possible through wireless technology to organise remote testing of your hot and cold water services so you do not need to go up in the roof or to the plant room any more.
If you want to know more – please ring.