The investment needed to fund greenfield developments of almonds, citrus, cotton and grapes could soon dry up because of a lack of water in the Murray Darling Basin, a leading water market economist has warned.

Chris Olszak, a director at water market consultancy Aither, said the expansion of water-intensive tree crops, cotton and grapes in NSW, Victoria and South Australia had been "a great news story" to date but that "water scarcity is starting to bite".