Context : Dwarf galaxies found in isolation in the Local Group ( LG ) are unlikely to have interacted with the large LG spirals , and therefore environmental effects such as tidal and ram-pressure stripping should not be the main drivers of their evolution . Aims : We aim to provide insight into the internal mechanisms shaping LG dwarf galaxies by increasing our knowledge of the internal properties of isolated systems . Here we focus on the evolved stellar component of the Aquarius dwarf galaxy , whose kinematic and metallicity properties have only recently started to be explored . Methods : Spectroscopic data in the region of the near-infrared Ca II triplet lines has been obtained with FORS2 at the Very Large Telescope for 53 red giant branch ( RGB ) stars . These data are used to derive line-of-sight velocities and [ Fe/H ] of the individual RGB stars . Results : We have derived a systemic velocity of -142.2 ^ { +1.8 } _ { -1.8 } km s ^ { -1 } , in agreement with previous determinations from both the HI gas and stars . The internal kinematics of Aquarius appears to be best modelled by a combination of random motions ( l.o.s . velocity dispersion of 10.3 ^ { +1.6 } _ { -1.3 } km s ^ { -1 } ) and linear rotation ( with a gradient -5.0 ^ { +1.6 } _ { -1.9 } km s ^ { -1 } arcmin ^ { -1 } ) along a P.A . = 139 _ { -27 } ^ { +17 } deg , broadly consistent with the optical projected major axis . This rotation signal is significantly misaligned or even counter-rotating to that derived from the HI gas . We also find the tentative presence of a mild negative metallicity gradient and indications that the metal-rich stars have a colder velocity dispersion than the metal-poor ones . Conclusions : This work represents a significant improvement with respect to previous measurements of the RGB stars of Aquarius , as it doubles the number of member stars already studied in the literature . We speculate that the misaligned rotation between the HI gas and evolved stellar component might have been the result of recent accretion of HI gas , or re-accretion after gas-loss due to internal stellar feedback .