Top panel: 1835 GHz OH triplet (blue line and grey histogram), overlaid with the 1838 GHz triplet (green line). Middle panel: the 1838 GHz OH triplet (green line and grey histogram), overlaid with the 1835 GHz triplet (blue line). Bottom panel: the 2514 GHz OH triplet (dark grey and grey histograms), overlaid with the 1838 GHz (green line) and 1835 GHz (blue line) triplets. In all panels, the lines were observed at the Cep A HW2 position, indicated in Fig. 1, and the three components of the triplets are indicated in the same colour as the considered triplet: see Tables 1 and 2. The vertical dashed line is at the ν_lsr of the cloud (− 11.2 km s^-1; e.g. Narayanan & Walker 1996; Gómez et al. 1999). In the top and middle panels, the spatial and spectral resolutions are 16.̋3 and 1.25 km s^-1, respectively. In the bottom panel, they are 11.̋9 and 0.91 km s^-1.