On 7 August 1896 the tunnel's inlet valve was opened by the Governor of South Australia, Sir Thomas Fowell Buxton and the reservoir began filling.
Within the suburb is the Happy Valley Reservoir accompanied by South Australia's largest water treatment plant, responsible for supplying water to much of the Adelaide metropolitan area.
O'Halloran Hill housing is a wedge shaped division which, apart from its southern boundary with Reynella East is isolated from other suburban housing by the Glenthorne Estate and the Happy Valley Reservoir that has resulted in a relatively low crime rate in comparison to surrounding suburbs.
Las Vegas Valley | Happy Days | Death Valley | Silicon Valley | San Fernando Valley | Squaw Valley, Placer County, California | Squaw Valley | reservoir | Shenandoah Valley | Willamette Valley | Happy Chandler | Valley of the Kings | Tennessee Valley Authority | Happy Valley | San Joaquin Valley | Rio Grande Valley | Rift Valley Province | Hudson Valley | Central Valley | Death Valley National Park | Death Valley Days | Coachella Valley Music and Arts Festival | Valley Forge | Klang Valley | Imperial Valley | Happy Mondays | Green Valley | valley | The Big Valley | San Gabriel Valley |
The catchment area of the Field River includes the Happy Valley Reservoir, part of Main South Road and the Southern Expressway and covers a total area of 55.3 km2.