▁By ▁ 1 9 2 4 , ▁the ▁company ▁were ▁supp lying ▁an ▁area ▁of ▁ ▁bounded ▁on ▁the ▁south ▁by ▁the ▁River ▁Th ames , ▁on ▁the ▁north ▁by ▁the ▁River ▁Cr ouch , ▁and ▁stretch ing ▁west wards ▁to ▁the ▁out sk ir ts ▁of ▁Sh en field . ▁As ▁the ▁volume ▁of ▁water ▁required ▁increased , ▁additional ▁well s ▁were ▁s unk , ▁until ▁there ▁were ▁ 3 6 ▁well s ▁or ▁bore hol es ▁in ▁operation . ▁They ▁pen etr ated ▁a ▁layer ▁of ▁London ▁cl ay ▁near ▁the ▁surface , ▁and ▁continued ▁into ▁the ▁s ands ▁of ▁the ▁Lower ▁London ▁t ert i ary ▁depos its ▁below ▁that , ▁but ▁the ▁yields ▁obtained ▁were ▁generally ▁poor ▁and ▁gradually ▁dimin ished ▁over ▁time . ▁In ▁ 1 9 2 1 ▁the ▁company ▁started ▁to ▁look ▁at ▁extract ing ▁water ▁from ▁rivers , ▁but ▁failed ▁to ▁obtain ▁parliament ary ▁appro val ▁for ▁a ▁joint ▁scheme ▁with ▁the ▁South ▁Es sex ▁Water works ▁Company ▁to ▁obtain ▁water ▁from ▁the ▁River ▁St our ▁on ▁the ▁border ▁between ▁Es sex ▁and ▁Su ff olk . ▁They ▁therefore ▁developed ▁a ▁scheme ▁to ▁extract ▁water ▁from ▁the ▁River ▁Black water , ▁the ▁River ▁Ch el mer ▁and ▁its ▁trib ut ary , ▁the ▁River ▁Ter . ▁An ▁Act ▁of ▁Parliament ▁was ▁obtained ▁in ▁August ▁ 1 9 2 4 , ▁to ▁enable ▁construction ▁of ▁Lang ford ▁Works , ▁to ▁the ▁west ▁of ▁M ald on . ▁ ▁The ▁project ▁involved ▁the ▁construction ▁of ▁int akes