Determination of PACS’s effective spectral resolution R over its spectral range using water emission lines. Upper panel: the colored dots show the ratios of the effective resolvable difference in wavelength and the resolvable difference in wavelength given by PACS’s spectral resolution for point sources determined from the detected water emission lines. The dots are color-coded by PACS’s spectral band they fall into. The solid black line shows a second-order polynomial fit to the data. Lower panel: PACS’s resolution for point sources in each spectral band, as given in the observer’s manual (ESA 2013) is shown using dashed lines, and the effective spectral resolution of the Jupiter observations as determined from the polynomial fit is plotted using solid lines.