The dam created a million gallon reservoir which was used to provide water to the navvies village below. It also supplied water to storage tanks used by locomotives, steam cranes and other steam driven machinery.
By 1905 the water works were complete, the Nant-y-Gro dam was no longer needed because the Elan village obtained water from the new water works scheme. The dam became redundant and almost forgotten.
In 1939 as war clouds gathered Barnes Neville Wallis was considering an engineering solution and the possibility of using explosives on structures, such as dams.