The main purpose of the dam is for potable water supply of the Toowoomba region.

From a catchment area of 169 square kilometres (65 sq mi), the dam creates an unnamed reservoir, with a surface area of 301 hectares (740 acres) at a maximum depth of 12.5 metres (41 ft) when at full capacity.

[3] Cooby Dam's lowest usable storage volume was recorded at 8% in January 2010.

[2] In July 2006, public outcry and a referendum with winning "No" vote rejected plans to place recycled water into Cooby Dam.

[citation needed] In 2007, the idea was again resurrected when plans for an advanced water treatment plant to be built near Cooby Dam by the Toowoomba City Council were suggested.