Upper: subregion of the observed 557 GHz H₂O map of ρ Oph A. The scales of υ_LSR and T_A are shown in the upper right corner. The Herschel beam at FWHM is indicated in the lower right corner (38′′, grey). The red circle shows the size of the Bonnor-Ebert sphere model of SM 1N discussed in the text. Lower: theoretical line profiles (red) are compared with the observed profiles (histograms). The spectra are half-beam spaced. The intensity is given in the T_mb scale, where η_mb = 0.62. The absorption dip is centred on υ_LSR = +3.3 km s^-1.