Mount Bold Reservoir is the largest reservoir in South Australia with a maximum capacity of over forty-six thousand megalitres. Costing A$1.1 million, the reservoir took six years to construct on the Onkaparinga River system between 1932 and 1938. The reservoir does not connect directly to the main reticulation system; rather, to maintain levels at Clarendon Weir, water is released only as required. Much of the water from Mount Bold will eventually end up at Happy Valley Reservoir and used to supply parts of the Mount Lofty Ranges and also Adelaide.