Can I have one single molecule of water? Is it possible detach one single molecule of water into vacuum lab?
 A: One can certainly separate water molecules at low temperature on a surface, as demonstrated by STM images. In Hossain et al. 2003 they show that the molecules stick to C defects on the surface. In (Shin et al 2010) they have nicer pictures of dissociated molecules on the surface. 
I suspect one can also make free-flying vacuum molecules simply by having heated water evaporate in vacuum and sending the thin vapor through filters and turbomolecular pumps in the right direction. It is easier to capture and control a charged object, but I see no technical reason why one could not get a single molecule. One might also use optical tweezers to bring togeher a $H^+$ and a $OH^-$ and build on from scratch.
Hossain, M. Z., Yamashita, Y., Mukai, K., & Yoshinobu, J. (2003). Model for C defect on Si (100): The dissociative adsorption of a single water molecule on two adjacent dimers. Physical Review B, 67(15), 153307.
Shin, H.-J., Jung, J., Motobayashi, K., Yanagisawa, S., Morikawa, Y., Kim, Y., & Kawai, M. (2010). State-selective dissociation of a single water molecule on an ultrathin MgO film. Nature Materials, 9(5), 442–447. doi:10.1038/nmat2740 
A: The closest I am aware of is trapping a single molecule inside a Buckyball.  The strong dipole moment of water makes it sticky, so I don't think the usual methods via optical tweezers work too well.  See Science, 29 July 2011, page 613 ff.
