1999A&A...343L..83L

Iso-Lws observations towards a large number of different positions in the core of the ρ Oph are used to place a limit to the abundance of wide spread H₂O. From Nlte excitation and radiative transfer modelling the average line spectrum of the ρ Oph, we find X(H₂O)<10^–6 to 10^–5. We interprete these results within the framework of the dynamical chemistry models by Bergin, Melnick & Neufeld (1998ApJ...499..777B), which describe the time evolution of molecular clouds being shocked by outflowing gas from young stellar objects, and conclude that the ρ Oph has been forming stars for less than one million years (2-5x10⁵yr). Finally, we show that this limiting result can be put to conclusive observational test by the Odin satellite mission in the near future.