Effect of finite resolving power on water lines. The red curve corresponds to a line-by-line model (with a resolution of R ~ 10⁶). From the light green curve to the purple curve, we show the same spectrum convolved with Gaussian LSF corresponding to the following resolving powers: at R = 50 000 (GIANO), at R = 75 000 (similar to CARMENES), at R = 115 000 (HARPS/-N), and at R = 134 000 (ESPRESSO). At the lowest resolving power, the individual molecular lines are not entirely resolved.