Terrestrial and sub-Neptune planets are expected to form in the inner (less than 10 AU) regions of protoplanetary disks¹. Water plays a key role in their formation^(2-4), although it is yet unclear whether water molecules are formed in situ or transported from the outer disk^(5,6). So far Spitzer Space Telescope observations have only provided water luminosity upper limits for dust-depleted inner disks⁷, similar to PDS 70, the first system with direct confirmation of protoplanet …