Ratio of H₂O 1₁₀–1₀₁/CO 3–2 line intensities as a function of absolute velocity for all sources. All spectra have been centred at 0 km s^-1. The top panel shows the ratio for all line wings where both H₂O and CO emission exceeds 4σ. Red-shifted line wings are shown in red and blue-shifted wings in blue. The average value is shown in black. The bottom panel shows the average value with the standard deviation shown in grey. The average values for the red- and blue-shifted line wings are shown in red and blue, respectively. The average ratios are taken in 1 km s^-1 bins.