This disease does not pass from person to person. I believe certain areas of Edinburgh are affected - google to see what these are in relation to your hotel. Make your decision based on that and, of course your gut instinct.

Something linked to water and aircon?

Yes, I think it is an airbourne thing. 

Not quite.  It only becomes semi airbourne when a venilation unit picks up small microbes of infected water and transfer is that way. 
It cannot be caught person to person nor from another person.  It is normally caught when drinking and accidently inhaling some of the water droplets into the lungs..  Just drinking the water will not cause you to catch it but most of us do inhale small particles of water when drinking. 

They have now closed down the infected water tower although it will be a few days before all the pipes are clear of any infection whatsoever.  It also seems to be concentrated in the West of the city so as long as you are not going there you will be fine

But drinking Distilled water will safe guard you then if tap water is the cause.

You also inhale water particles when having a shower or bath