Water: from clouds to planets
  Results from recent space missions, in particular Spitzer and Herschel, have
lead to significant progress in our understanding of the formation and
transport of water from clouds to disks, planetesimals, and planets. In this
review, we provide the underpinnings for the basic molecular physics and
chemistry of water and outline these advances in the context of water formation
in space, its transport to a forming disk, its evolution in the disk, and
finally the delivery to forming terrestrial worlds and accretion by gas giants.
Throughout, we pay close attention to the disposition of water as vapor or
solid and whether it might be subject to processing at any stage. The context
of the water in the solar system and the isotopic ratios (D/H) in various
bodies are discussed as grounding data point for this evolution. Additional
advances include growing knowledge of the composition of atmospheres of
extra-solar gas giants, which may be influenced by the variable phases of water
in the protoplanetary disk. Further, the architecture of extra-solar systems
leaves strong hints of dynamical interactions, which are important for the
delivery of water and subsequent evolution of planetary systems. We conclude
with an exploration of water on Earth and note that all of the processes and
key parameters identified here should also hold for exoplanetary systems.
