  Characterising the atmospheres of hot Jupiters is important in understanding
the formation and migration of these exotic planets. However, there are still
many open questions about the chemical and physical properties of these
atmospheres. Here, we confirm the detection of water vapour in thermal emission
from the non-transiting hot Jupiter {\tau} Bootis Ab with the high resolution
NIR CARMENES spectrograph. Combining over 17 h of observations (560 spectra)
and using a Bayesian cross-correlation to log-likelihood approach, we measure a
systemic velocity of $V_{sys} = -11.51^{+0.59}_{-0.60}$ km/s and a radial
velocity semi-amplitude of $K_{P} = 106.21^{+1.76}_{-1.71}$ km/s for the
planet, which results in an absolute mass of $M_{P} = 6.24^{+0.17}_{-0.18}
M_{J}$ and an orbital inclination of $41.6^{+1.0}_{-0.9}$ degrees. Our
retrieved $V_{sys}$ shows a significant shift (+5 km/s) from the literature
value, which could be caused by an inaccurate time of periastron. Within the
explored model grid, we measure a preference for solar water abundance (VMR =
$10^{-3}$) and no evidence for additional minor species in the atmosphere.
Given the extensive orbital coverage of the data, we searched for a phase
dependency in the water signal but found no strong evidence of variation with
orbital phase. This detection is at odds with recent observations from
SPIRou/CFHT and their tight upper limit on water abundance. We recommend
further observations of the atmosphere {\tau} Bootis Ab to try and resolve
these discrepancies.
