Vampires in my modern-day urban fantasy setting, to varying degrees, have a weakness to both sunlight and open water. The celestial energies Earth radiates out from its core take on different properties depending on what non-gaseous material they last passed through. If it was more than three feet of liquid water followed by less than three feet of any other non-gaseous matter, it will be as if a vampire were standing in direct sunlight. And depending on the strength of the vampire in question, exposure to sunlight or open water alone ranges from debilitating to dangerous, and both simultaneously is outright lethal to all but the most powerful vampires on earth.
These rules, you may notice, still leave a vampire vulnerable to underground sources of water, as long as the water is deep enough and the ground between them and the water is thin enough. Which leaves open the interesting possibility that vampires' enemies might take advantage of this to take recently-turned vampires by surprise and trick them into walking into an area they don't realize qualifies as "open water".
But of course, doing something like digging a moat and putting a tarp over it or things of that like would be fairly obvious. What I'm interested in is what sorts of pre-existing parts of modern-day life are already dangerous to vampires, and could likely catch a vampire off-guard even when they know they're supposed to steer clear of open water.
What location in a modern-day society would a new vampire be most likely to not realize qualifies as standing over open water?