( ( ( Always ( filter ( or ( boil water ) ) ) ) ( since ( ( Giardia or ) ( other pathogens ) ) ) ) ( ( may ( be present ) ) . ) )
(ROOT (S (NP (NP (NNP Always) (NN filter) (CC or) (NN boil) (NN water)) (PP (IN since) (NP (NP (NNP Giardia)) (CC or) (NP (JJ other) (NNS pathogens))))) (VP (MD may) (VP (VB be) (ADJP (JJ present)))) (. .)))
Always filter or boil water since Giardia or other pathogens may be present.
(ROOT (S (NP (NNP Water)) (VP (MD can) (VP (VB be) (VP (VBN boiled) (S (VP (TO to) (VP (VB kill) (NP (NP (NN giardia)) (CC and) (NP (RBS most) (JJ other) (NNS pathogens))))))))) (. .)))