Context. Water is a key molecule in the star formation process, but its spatial distribution in star-forming regions is not well known.Aims. We study the distribution of dust continuum and H_{2_{O and ^{13^{CO line emission in DR21, a luminous star-forming region with a powerful outflow and a compact H ii region.Methods. Herschel-HIFI spectra near 1100 GHz show narrow ^{13^{CO 10–9 emission and H_{2_{O 1_{11_{–0_{00_{absorption from the dense core and broad emission from the outflow in both lines. The H_{2_{O line also shows absorption by a foreground cloud known from ground-based observations of low-J CO lines.Results. The dust continuum emission is extended over 36” FWHM, while the ^{13^{CO and H_{2_{O lines are confined to ≈24” or less. The foreground absorption appears to peak further North than the other components. Radiative transfer models indicate very low abundances of ~2×10^{-10^{for H_{2_{O and ~8×10^{-7^{for ^{13^{CO in the dense core, and higher H_{2_{O abundances of ~4×10^{-9^{in the foreground cloud and ~7×10^{-7^{in the outflow.Conclusions. The high H_{2_{O abundance in the warm outflow is probably due to the evaporation of water-rich icy grain mantles, while the H_{2_{O abundance is kept down by freeze-out in the dense core and by photodissociation in the foreground cloud.}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}

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