Using the Submillimeter Array (SMA) on Mauna Kea, the {{{H}}}216{{O}} {10}{2,9}–9{}{3,6} transition ({E}{{up}} = 1863 K) at 321.2 GHz has been detected toward the embedded low-mass protostar HL Tau. The line centroid is blueshifted by 20 km s‑1 with respect to the source velocity, and it has a FWHM of 25 km s‑1. The emission is tentatively resolved and extends ∼3″–4″ over the sky (∼2 beams), or ∼500 au at the distance of Taurus. The velocity offset, and to a lesser degree the spatial extent of the emission, show that the line originates in the protostellar jet or wind. This result suggests that at least some water emission observed with Herschel and Spitzer toward embedded sources, and perhaps also disk sources, contains a wind or jet component, which is crucial for interpreting these data. These pathfinder observations done with the SMA open a new window into studying the origin of water emission with e.g., ALMA, thus providing new insights into where water is in protostellar systems.
