Mercury metal exposed to the atmosphere will (dependent on the specific location) soon gather dust particles upon it's surface if left undisturbed. In this state and at 23C the mercury will not evaporate into the atmosphere as the combination of dust and temperature will work against this. I'm talking about a very small spill, that one would have to get down upon hands and knees to visualize. Droplets in the order of less than 1mm.
In a previous job (9.5 years experience-senior technician) on extremely rare occasions had to either deal with small spills (onto the floor) or a yearly cleanup of old Mercury diffusion vacuum pumps (very hazardous because it involves actually heating at high temperature the Hg to help clean the pump- all conducted under stringent safety procedures and apparatus, to prevent any mercury from entering the atmosphere. When we tried to detect small mercury spills that had been in cracks in the flooring, it was not possible with a very sensitive mercury detector. However, if one jumped or caused large vibrations near the spill, it could be detected but only extremely close to the source. This is because a 'fresh surface" of mercury will have been exposed due to the vibrations moving the settled dust to different locations on the surface of the droplets.
So to answer your questions, will depend upon the conditions the mercury and water is subjected too. Boiling the water will definitely liberate Hg vapour! It is not that simple an answer. As stated above unless you understand the physical and chemical properties of Hg and it's interaction with the particular environment, better not to "experiment" with it. I suggest reading this: https://journals.aps.org/pr/abstract/10.1103/PhysRev.26.859