Might be right about leigonaires disease and airborn, but also in hot tubs and cooling towers etc, i would not use the 5 month old water, for safety reasons
idealrob
Rob, sertiously unlikey to be any danger with this for safety reasons, think this way:
Your garden hose, this in winter (unless your wft that most of us are, buggered up my example but will carry on)
people leave a garden hose sat all winter till the warmer weather, you never here of them getting leigonairs, there are factors that make this possible but not in a bottle water sat standing the chances would be slim to none, you have more chance catching it starting up a pressure washer that has not been used for years IMO