10$^{4}$ yr. @immer13 detected water masers toward W33 A (G012.90$-$0.24, G012.90$-$0.26) and W33 Main (G012.81$-$0.19) in a radial velocity (V$_\mathrm{lsr}$) range of 33–38 km s$^{-1}$, while the water masers in W33 B (G012.68$-$0.18) were observed in a velocity range of 57–63 km s$^{-1}$. Note that the radial velocity information has been found different for W33 B compared to W33 A and W33 Main. These authors suggested the kinematic distance of $\sim$3.7 kpc (corresponding to V$_\mathrm{lsr}$ of 36 km s$^{-1}$). They also reported the parallactic distance of the water masers in the massive star forming complex W33 (containing G012.68$-$0.18, G012.81$-$0.19, G012.90$-$0.24, G012.90$-$0.26) to be $\sim$2.4 kpc.

It was suggested that the distance estimated using the trigonometric parallax observations of maser sources is more reliable than the kinematic distance measurements [e.g., @reid09; @sato10; @immer13]. Hence, despite different V$_\mathrm{lsr}$ values, it has been considered that the sites (i.e., W33 A (G012.90$-$0.24, G012.90$-$0.26), W33 B (G012.68$-$0.18), and W33 Main (G012.81$-$0.19)) are located at the similar distance, and are part of the W33 complex [e.g., @immer13; @messineo15; @kohno18]. Based on the detection of methanol masers, @kohno18 also pointed out the presence of massive YSOs toward the sub-regions W33 Main, W33 A, and W33 B. Using 