▁Ab ber ton ▁Res er voir ▁covers ▁an ▁area ▁of ▁ ▁and ▁lies ▁in ▁the ▁valley ▁of ▁the ▁L ayer ▁Brook . ▁When ▁full , ▁it ▁could ▁hold ▁. ▁L ayer ▁treatment ▁works ▁could ▁process ▁ ▁per ▁day , ▁and ▁the ▁system ▁was ▁designed ▁to ▁store ▁water ▁from ▁winter ▁ra inf all ▁for ▁use ▁in ▁the ▁summer ▁months . ▁ ▁Const ruction ▁of ▁the ▁res er voir ▁began ▁in ▁March ▁ 1 9 3 6 ▁and ▁continued ▁until ▁the ▁start ▁of ▁the ▁Second ▁World ▁War ▁in ▁ 1 9 3 9 . ▁To ▁pass ▁under ▁the ▁River ▁Col ne , ▁sh aft s ▁were ▁constructed ▁on ▁either ▁side ▁of ▁the ▁river , ▁and ▁a ▁ ▁diameter ▁tunnel ▁was ▁exc av ated ▁between ▁the ▁sh aft s . ▁The ▁min ers ▁worked ▁in ▁com pressed ▁air , ▁and ▁tw in ▁pip es ▁of ▁ ▁diameter ▁were ▁run ▁through ▁the ▁tunnel . ▁The ▁original ▁pipeline ▁consisted ▁of ▁bit umen - lined ▁steel ▁tub es , ▁some ▁ ▁and ▁some ▁ ▁in ▁diameter . ▁A ▁second ▁pipeline ▁of ▁ ▁diameter ▁pip es ▁was ▁subsequently ▁installed . ▁F illing ▁of ▁the ▁res er voir ▁began ▁in ▁ 1 9 3 9 ▁and ▁was ▁completed ▁by ▁the ▁end ▁of ▁ 1 9 4 0 . ▁Some ▁minor ▁commission ing ▁work , ▁including ▁the ▁Ab ber ton ▁p ump ing ▁station , ▁was ▁delayed ▁until ▁the ▁end ▁of ▁host ilities . ▁The ▁project ▁cost ▁£ 5 0 0 , 0 0 0 . ▁Many ▁of ▁the ▁construction ▁workers ▁came