  Infrared spectroscopy over a wide spectral range and at the highest resolving
powers (R>70 000) has proved to be one of the leading technique to unveil the
atmospheric composition of dozens of exoplanets. The recently upgraded
spectrograph CRIRES instrument at the VLT (CRIRES+) was operative for a first
Science Verification in September 2021 and its new capabilities in atmospheric
characterisation were ready to be tested. We analysed transmission spectra of
the Hot Saturn WASP-20b in the K-band (1981-2394 nm) acquired with CRIRES+,
aiming at detecting the signature of H2O and CO. We used Principal Component
Analysis to remove the dominant time-dependent contaminating sources such as
telluric bands and the stellar spectrum and we extracted the planet spectrum by
cross-correlating observations with 1D and 3D synthetic spectra, with no
circulation included. We present the tentative detection of molecular
absorption from water-vapour at S/N equal to 4.2 and 4.7 by using only-H2O 1D
and 3D models, respectively. The peak of the CCF occurred at the same
rest-frame velocity for both model types (Vrest=-1 $\pm$ 1 kms$^{-1}$), and at
the same projected planet orbital velocity but with different error bands (1D
model: KP=131$^{+18}_{-29}$ kms$^{-1}$; 3D: KP=131$^{+23}_{-39}$ kms$^{-1}$).
Our results are in agreement with the one expected in literature (132.9 $\pm$
2.7 kms$^{-1}$). Although sub-optimal observational conditions and issues with
pipeline in calibrating and reducing our raw data set, we obtained the first
tentative detection of water in the atmosphere of WASP-20b. We suggest a deeper
analysis and additional observations to confirm our results and unveil the
presence of CO.
