providing a source of {HEAD ~ water} for flowing through a floway, said water containing a quantity of pollutants and having a pH lower than a pH of precipitation of said pollutants on {TAIL ~ entry} into said floway 
providing a source of { HEAD ~ water } for flowing through a floway , said water containing a quantity of pollutants and having a pH lower than a pH of precipitation of said pollutants on { TAIL ~ entry } into said floway
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH