  Single-dish spectra and interferometric maps of (sub)mm lines of H2O-18 and
HDO are used to study the chemistry of water in eight regions of high-mass star
formation. The spectra indicate HDO excitation temperatures of ~110 K and
column densities in an 11'' beam of ~2x10^14 cm^-2 for HDO and ~2x10^17 cm^-2
for H2O, with the N(HDO)/N(H2O) ratio increasing with decreasing temperature.
Simultaneous observations of CH3OH and SO2 indicate that 20-50% of the
single-dish line flux arises in the molecular outflows of these objects. The
outflow contribution to the H2O-18 and HDO emission is estimated to be 10-20%.
Radiative transfer models indicate that the water abundance is low (~10^-6)
outside a critical radius corresponding to a temperature in the protostellar
envelope of ~100 K, and `jumps' to H2O/H2 ~ 10^-4 inside this radius. This
value corresponds to the observed abundance of solid water and together with
the derived HDO/H2O abundance ratios of ~1/1000 suggests that the origin of the
observed water is evaporation of grain mantles. This idea is confirmed in the
case of AFGL 2591 by interferometer observations of HDO, H2O-18 and SO2 lines,
which reveal compact (~800 AU) emission with a systematic velocity gradient.
This size is similar to that of the 1.3 mm continuum towards AFGL 2591, from
which we estimate a mass of ~0.8 M0, or ~5% of the mass of the central star. We
speculate that we may be observing a circumstellar disk in an almost face-on
orientation.
