( ( ( ( Precipitation , ) runoff ) , ) ( ( groundwater flow ) . ) )
(ROOT (S (NP (NP (NNP Precipitation)) (, ,) (NP (NN runoff)) (, ,)) (VP (VBP groundwater) (NP (NN flow))) (. .)))
Precipitation, runoff, groundwater flow.
(ROOT (S (NP (NNP Groundwater)) (ADVP (RB primarily)) (VP (VBZ comes) (PP (IN from) (NP (NN precipitation)))) (. .)))