( They ( ( ( occur ( most often ) ) ( in ( ( ( mountain communities ) and ) ( those ( that ( get ( ( ( drinking water ) ( from ( ( streams or ) rivers ) ) ) ( without ( a ( water ( filtration system ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (VBP occur) (ADVP (RBS most) (RB often)) (PP (IN in) (NP (NP (NN mountain) (NNS communities)) (CC and) (NP (NP (DT those)) (SBAR (WHNP (WDT that)) (S (VP (VBP get) (S (VP (VBG drinking) (NP (NN water)) (PP (IN from) (NP (NNS streams) (CC or) (NNS rivers))) (PP (IN without) (NP (DT a) (NN water) (NN filtration) (NN system)))))))))))) (. .)))
They occur most often in mountain communities and those that get drinking water from streams or rivers without a water filtration system.
(ROOT (S (NP (NNS Streams)) (ADVP (RB often)) (VP (VBP start) (PP (IN in) (NP (NNS mountains)))) (. .)))