If its just the water tank, then from my experience no, the old car has it behind the passenger seat in full view, all I was asked was "is that a fuel tank? " when I explained they just asked for me to mark it clearly "Water" never been asked about it since in several different countries
The new car has it up front and I still get asked what it is for, why it doesn't have an earth on it as a fuel tank requires it etc,etc, think I need to mark that one water as well!!!
cheers Richie