  Inside the H$_{2}$O snowline of protoplanetary disks, water evaporates from
the dust-grain surface into the gas phase, whereas it is frozen out on to the
dust in the cold region beyond the snowline. H$_{2}$O ice enhances the solid
material in the cold outer part of a disk, which promotes the formation of
gas-giant planet cores. We can regard the H$_{2}$O snowline as the surface that
divides the regions between rocky and gaseous giant planet formation. Thus
observationally measuring the location of the H$_{2}$O snowline is crucial for
understanding the planetesimal and planet formation processes, and the origin
of water on Earth. In this paper, we find candidate water lines to locate the
H$_{2}$O snowline through future high-dispersion spectroscopic observations.
First, we calculate the chemical composition of the disk and investigate the
abundance distributions of H$_{2}$O gas and ice, and the position of the
H$_{2}$O snowline. We confirm that the abundance of H$_{2}$O gas is high not
only in the hot midplane region inside the H$_{2}$O snowline but also in the
hot surface layer of the outer disk. Second, we calculate the H$_{2}$O line
profiles and identify those H$_{2}$O lines which are promising for locating the
H$_{2}$O snowline: the identified lines are those which have small Einstein $A$
coefficients and high upper state energies. The wavelengths of the candidate
H$_{2}$O lines range from mid-infrared to sub-millimeter, and they overlap with
the regions accessible to ALMA and future mid-infrared high dispersion
spectrographs (e.g., TMT/MICHI, SPICA).
