To prevent Legionella from occurring you need to understand the problem
The first step in preventing Legionella from occurring is to understand the problem. You need to identify every possible risk, from spa pools, to car washes and hot water systems to sprinklers – anywhere water is used that might produce a mist or spray that can be inhaled is a risk. How big the risk is depends on who might be exposed as the elderly, those with underlying health problems and smokers are all more vulnerable to the disease – so hospitals and nursing homes need to be especially careful (read more on Legionella in hospital and care homes here) . But water which sits stagnant in dead-legs of unused pipes are a particular problem, too, so hotel rooms or villas sitting empty for a few weeks can become a problem. The rapid test is helpful here – letting you quickly get a picture of the condition of your system or establish how widespread a problem is. You should really test every separate water system to start with, and on large systems at multiple locations, for example, one test per floor.
The other major contributor to bacteria colonising a water system is how clean the water, tanks and pipe work are.
If there is visible slime, sludge, rust or scale in a system, it will be almost impossible to guarantee Legionnella can’t grow and a much more regular testing programme will be required (possibly every week) until remedial action can be taken to clean or replace the affected areas.
How to control Legionella risks
There are two main approaches to controlling Legionella. Firstly, temperature: keeping hot water hot and cold water cold. The hot water should quickly get to over 55 degree C when you turn on any tap in the building. If it doesn’t, the bacteria can survive. However, you need to be aware of the risk of scalding so the water temperature needs to be tightly controlled. In most part of the world, cold water supplies are too cold for Legionella to grow, but in Dubai it’s quite possible that the temperature can exceed 20 degree C – in which case you are into the danger zone. Monitoring the temperatures is the first line of defence against Legionella in hot and cold water systems (most experts suggest monthly monitoring). When they fall outside the limit, it is a good time to test for Legionella.
The other approach to control is to add a biocide to the water, like chlorine, chlorine dioxide or copper and silver ions. Regular testing is required to ensure the dosing is correct, and Legionella testing should be used as a backup if it is not. Even with a good biocide control programme, many building managers like to do monthly Legionella tests, especially in the first year until they build up confidence in the control system; if they manage a whole year without a positive result, they may reduce the frequency of testing or the number of places they take samples from.