Histogram of the sizes of H₂O maser components exceeding the observational error (s_υ > σ_s). The ordinate shows the number of components per size bin. The thickest black line shows the distribution for the epoch with the brightest maximum emission (I_max, given in Table 2) for each star, with thinner and paler/bluer lines representing epochs with progressively fainter maxima. A few U Her and U Ori components with sizes  > 40 mas are not shown.