You should assume any stagnant water flushed may contain Legionella bacteria, and you need to avoid exposing yourself or others to this flushed water. Seek an expert.
If any flushing takes place then it should be done in a manner that avoids producing a water aerosol. As an example you can control some aerosols by placing towels over outlets or discharging outside taps or shower heads into a refuse sack.
Dependant on the design of your water system there could be a number of flushing methods.
Think about how water normally flows through your building. Where the hot and cold water supplies come from, are there cold water tanks, hot water vessels, hot water circulation systems, point of use water heaters and outside taps.
Once you know how hot and cold is distributed through your building and what any tanks serve, it can be a good idea to flush outlets nearest those sources drawing fresh hot and cold water for a few minutes. Then close those outlets and systematically moving through the building drawing fresh water as you go working towards the furthest points away from those hot and cold sources. It is probably better to work on one system at a time but this can get complicated. If you're not sure then seek expert advice (don't forget to operate appliances too).
Sources of supply
Cold water sources
- Water Main - This could be directly from the public main and without any onsite cold water tanks, in which case you should start drawing water from outlets closest to the incoming supply or main internal stop valve.
- Tanks - Any tank should be cleaned and disinfected before you attempt drawing water from it – you don't want to draw any additional stagnant water through your water systems. (Seek expert advice). Once the tank is clean, determine the flushing plan to draw water from outlets nearest that tank and working towards outlets furthest away.
Hot water sources
If the hot water vessel / system has been used less than normal for a week or more then it's likely to contain Legionella. The first step is to take expert advice on how to disinfect the vessel and system. Once disinfected hot water should then be drawn systematically through the system (nearest to furthest outlets), until fresh hot water is drawn through for at least a minute at each hot outlet.