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Apart from being an important coolant, H2O is known to be a tracer ofhigh-velocity molecular gas. Recent models predict relatively high abundancesbehind interstellar shockwaves. The dynamical and physical conditions of theH2O emitting gas, however, are not fully understood yet. We aim to determinethe abundance and distribution of H2O, its kinematics and the physicalconditions of the gas responsible for the H2O emission. The observed lineprofile shapes help us understand the dynamics in molecular outflows. We mappedthe VLA1623 outflow, in the ground-state transitions of o-H2O, with the HIFIand PACS instruments. We also present observations of higher energy transitionsof o-H2O and p-H2O obtained with HIFI and PACS towards selected outflowpositions. From comparison with non-LTE radiative transfer calculations, weestimate the physical parameters of the water emitting regions. The observedwater emission line profiles vary over the mapped area. Spectral features andcomponents, tracing gas in different excitation conditions, allow us toconstrain the density and temperature of the gas. The H2O emission originatesin a region where temperatures are comparable to that of the warm H2 gas(T\gtrsim200K). Thus, the H2O emission traces a gas component significantlywarmer than the gas responsible for the low-J CO emission. The H2O columndensities at the CO peak positions are low, i.e. N(H2O) \simeq (0.03-10)x10e14cm-2. The H2O abundance with respect to H2 in the extended outflow is estimatedat X(H2O)<1x10e-6, significantly lower than what would be expected from mostrecent shock models. The H2O emission traces a gas component moving atrelatively high velocity compared to the low-J CO emitting gas. However, otherdynamical quantities such as the momentum rate, energy and mechanicalluminosity are estimated to be the same, independent of the molecular tracerused, CO or H2O.

H2O line mapping at high spatial and spectral resolution - Herschel observations of the VLA1623 outflow