{HEAD ~ The O ring} prevents {TAIL ~ water} from otherwise flowing through the channel and externally of the water filtration system 
prevents
{ HEAD ~ The O ring } prevents { TAIL ~ water } from otherwise flowing through the channel and externally of the water filtration system
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH