(S (S (BASENP (NN Groundwater)) (VP (VP (VP (VBZ is) (NP (BASENP (DT the) (JJ primary) (NN source)) (PP (IN of) (NP (BASENP (NN water)) (PP (IN for) (BASENP (NN drinking) (CC and) (NN irrigation))))))) (CONJP (COMMA ,) (CC but)) (VP (VBZ has) (VP (VBN been) (ADJP (JJ difficult) (S (VP (TO to) (VP (VB exploit)))))))) (CC and) (VP (VBZ is) (ADJP (RB often) (JJ contaminated))))) (PERIOD .))