Context : The outflow driven by the low-mass class 0 protostar L1157 is the prototype of the so-called chemically active outflows .
The bright bowshock B1 in the southern outflow lobe is a privileged testbed of magneto-hydrodynamical ( MHD ) shock models , for which dynamical and chemical processes are strongly interdependent .

Aims : We present the first results of the unbiased spectral survey of the L1157-B1 bowshock , obtained in the framework of the key program ” Chemical Herschel Surveys of Star Forming Regions ” ( CHESS ) .
The main aim is to trace the warm and chemically enriched gas and to infer the excitation conditions in the shock region .

Methods : The CO 5-4 and o-H _ { 2 } O 1 _ { 10 } -1 _ { 01 } lines have been detected at high-spectral resolution in the unbiased spectral survey of the HIFI-Band 1b spectral window ( 555-636 GHz ) , presented by Codella et al .
in this volume .
Complementary ground-based observations in the submm window help establish the origin of the emission detected in the main-beam of HIFI , and the physical conditions in the shock .

Results : Both lines exhibit broad wings , which extend to velocities much higher than reported up to now .
We find that the molecular emission arises from two regions with distinct physical conditions : an extended , warm ( 100 \hbox { \kern 2.0 ptK } ) , dense ( 3 \times 10 ^ { 5 } \hbox { \kern 2.0 ptcm$ { } ^ { -3 } $ } ) component at low-velocity , which dominates the water line flux in Band 1 ; a secondary component in a small region of B1 ( a few arcsec ) associated with high-velocity , hot ( > 400 \hbox { \kern 2.0 ptK } ) gas of moderate density ( ( 1.0 - 3.0 ) \times 10 ^ { 4 } \hbox { \kern 2.0 ptcm$ { } ^ { -3 } $ } ) , which appears to dominate the flux of the water line at 179 \hbox { \kern 2.0 pt$ \mu$m } observed with PACS .
The water abundance is enhanced by two orders of magnitude between the low- and the high-velocity component , from 8 \times 10 ^ { -7 } up to 8 \times 10 ^ { -5 } .
The properties of the high-velocity component agree well with the predictions of steady-state C-shock models .

Conclusions :