Histograms of the maser isotropic luminosity for a maximum maser luminosity of 300 Jy kpc² (main) and 30 Jy kpc² (inset). Less than 4% of the observed masers have an isotropic luminosity higher than 300 Jy kpc². The bins are 10 and 1 Jy kpc² for the histograms in the main plot and in the inset, respectively. The histogram values are normalized by the total number of selected water masers. The continuous blue and black lines show the power-law fits of the values of the histograms in the main plot and in the inset, respectively, and the best-fit expressions are also reported using the same colors of thecorresponding fits.