Panel (a): a replotted figure of the right panel of Figure 1 in Zhang et al. (2023) to show the maser distribution in W51-North. The light-colored circles and dark-colored squares represent the H₂O maser spots detected in our VLA observation and that in Imai et al. (2002), respectively. The reference position is R.A. (J2000) = 19^h23^m40.ˢ047, decl. (J2000) = +14°31﹩{}^{{\prime} }﹩05.″530. The 1.3 mm continuum detected in the archival ALMA data is shown with dark blue contours, with the start, end, and step levels to be 0.0025, 0.0100, and 0.0025 Jy beam⁻¹, respectively. The “A,” “B,” and “C” labels mark the regions that have shown variations, as shown in Figure 5 in Zhang et al. (2023). Panel (b): the spectra of H₂O maser transition extracted from W51-IRS2, W51-North, and W51d2 regions detected with the VLA. The red dashed lines at ∼58 km s⁻¹ in panels (b) and (d) mark the strongest velocity component in the W51d2 subregion. Panel (c): the spatial distribution of H₂O maser spots in the whole region of W51-IRS2. Panel (d): the spectra of H₂O maser transition detected toward W51-IRS2 using TMRT from 2020 January 8 to April 7, which was taken from Zhang et al. (2022).