Context :

Aims : We investigate the effect of the physical environment on water and ammonia abundances across the S140 photodissociation region ( PDR ) with an embedded outflow .

Methods : We have used the Odin satellite to obtain strip maps of the ground-state rotational transitions of ortho -water and ortho -ammonia , as well as CO ( 5 – 4 ) and ^ { 13 } CO ( 5 – 4 ) across the PDR , and H _ { 2 } ^ { 18 } O in the central position .
A physi-chemical inhomogeneous PDR model was used to compute the temperature and abundance distributions for water , ammonia and CO. A multi-zone escape probability method then calculated the level populations and intensity distributions .
These results are compared to a homogeneous model computed with an enhanced version of the RADEX code .

Results : H _ { 2 } O , NH _ { 3 } and ^ { 13 } CO show emission from an extended PDR with a narrow line width of \sim 3 km s ^ { -1 } .
Like CO , the water line profile is dominated by outflow emission , however , mainly in the red wing .
Even though CO shows strong self-absorption , no signs of self-absorption are seen in the water line .
H _ { 2 } ^ { 18 } O is not detected .
The PDR model suggests that the water emission mainly arises from the surfaces of optically thick , high density clumps with n ( \mathrm { H _ { 2 } } ) \ga 10 ^ { 6 } cm ^ { -3 } and a clump water abundance , with respect to H _ { 2 } , of 5 \times 10 ^ { -8 } .
The mean water abundance in the PDR is 5 \times 10 ^ { -9 } , and between \sim 2 \times 10 ^ { -8 } – 2 \times 10 ^ { -7 } in the outflow derived from a simple two-level approximation .
The RADEX model points to a somewhat higher average PDR water abundance of 1 \times 10 ^ { -8 } .
At low temperatures deep in the cloud the water emission is weaker , likely due to adsorption onto dust grains , while ammonia is still abundant .
Ammonia is also observed in the extended clumpy PDR , likely from the same high density and warm clumps as water .
The average ammonia abundance is about the same as for water : 4 \times 10 ^ { -9 } and 8 \times 10 ^ { -9 } given by the PDR model and RADEX , respectively .
The differences between the models most likely arise due to uncertainties in density , beam-filling and volume filling of clumps .
The similarity of water and ammonia PDR emission is also seen in the almost identical line profiles observed close to the bright rim .
Around the central position , ammonia also shows some outflow emission although weaker than water in the red wing .
Predictions of the H _ { 2 } O 1 _ { 1 , 0 } – 1 _ { 0 , 1 } and 1 _ { 1 , 1 } – 0 _ { 0 , 0 } antenna temperatures across the PDR are estimated with our PDR model for the forthcoming observations with the Herschel Space Observatory .

Conclusions :