Observed OPR of H₂O⁺ versus the cosmic-ray ionisation rates derived using the steady-state analysis of the OH⁺ and H₂O⁺. The results from this work are marked by teal pentagons while the blue diamonds and black triangles display the results for sight lines studied in the Milky Way by Indriolo et al. (2015) and Jacob et al. (2020). For comparison we display the OPR of H₂O⁺ also derived by Indriolo et al. (2015) towards Galactic centre (GC) sight lines using purple stars. The dashed red line marks the equilibrium OPR value of three.