Far-infrared spectroscopy reveals gas cooling and its underlying heating due to physical processes taking place in the surroundings of protostars . These processes are reflected in both the chemistry and excitation of abundant molecular species . Here , we present the Herschel -PACS far-IR spectroscopy of 90 embedded low-mass protostars from the WISH [ van Dishoeck \etal ( 2011 ) , ( van Dishoeck et al . 2011 ) ] , DIGIT [ Green \etal ( 2013 ) , ( Green et al . 2013 ) ] , and WILL surveys [ Mottram \etal ( 2017 ) , ( Mottram et al . 2017 ) ] . The 5 \times 5 spectra covering the \sim 50 ^ { \prime \prime } \times 50 ^ { \prime \prime } field-of-view include rotational transitions of CO , H _ { 2 } O , and OH lines , as well as fine-structure [ O I ] and [ C II ] in the \sim 50-200 \mu m range . The CO rotational temperatures ( for J _ { \mathrm { u } } \geq 14 ) are typically \sim 300 K , with some sources showing additional components with temperatures as high as \sim 1000 K. The H _ { 2 } O / CO and H _ { 2 } O / OH flux ratios are low compared to stationary shock models , suggesting that UV photons may dissociate some H _ { 2 } O and decrease its abundance . Comparison to C shock models illuminated by UV photons shows good agreement between the line emission and the models for pre-shock densities of 10 ^ { 5 } cm ^ { -3 } and UV fields 0.1-10 times the interstellar value . The far-infrared molecular and atomic lines are the unique diagnostic of shocks and UV fields in deeply-embedded sources .