Two types of water property rights exist in the Murray Darling Basin: ground water and surface water. The latter has three distinct forms, high security, general security and supplementary. Their value is dependent on location and ability to supply water under known climate signals. This article suggests an optimal mix of property rights to allow the Basin Plan to achieve its objectives in obtaining 3,200 gigalitres of surface water. However, the solution exposes the Basin Plan’s hidden gift of gold to irrigators, an extra 929 gigalitres of ground water extractions. The value of this gift increases under a changing climate.