  We report ALMA high-resolution observations of water emission lines
$p-{\rm{H_2O}} (2_{02}-1_{11}$), $o-{\rm{H_2O}} (3_{21}-3_{12})$,
$p-{\rm{H_2O}} (4_{22}-4_{13})$, in the strongly lensed galaxy
HATLASJ113526.2-01460 at redshift z $\sim$ 3.1. From the lensing-reconstructed
maps of water emission and line profiles, we infer the general physical
properties of the ISM in the molecular clouds where the lines arise. We find
that the water vapor lines $o-{\rm{H_2O}} (3_{21}-3_{12})$, $p-{\rm{H_2O}}
(4_{22}-4_{13})$ are mainly excited by FIR pumping from dust radiation in a
warm and dense environment, with dust temperatures ranging from 70 K to $\sim
100$ K, as suggested by the line ratios. The $p-{\rm{H_2O}} (2_{02}-1_{11})$
line instead, is excited by a complex interplay between FIR pumping and
collisional excitation in the dense core of the star-forming region. This
scenario is also supported by the detection of the medium-level excitation of
CO resulting in the line emission CO (J=8-7). Thanks to the unprecedented high
resolution offered by the combination of ALMA capabilities and gravitational
lensing, we discern the different phases of the ISM and locate the hot
molecular clouds into a physical scale of $\sim$ 500 pc. We discuss the
possibility of J1135 hosting an AGN in its accretion phase. Finally, we
determine the relation between the water emission lines and the total IR
luminosity of J1135, as well as the SFR as a function of water emission
intensities, comparing the outcomes to local and high-$z$ galactic samples from
the literature.
