I will argue that The Grapes of Wrath represents an indictment of the American myth of the garden and its accompanying myth of the frontier. The lever with which Steinbeck pries apart and ultimately dismantles these fictions is a critique of the agricultural practices that created the Dust Bowl and then metamorphosed into a new set of norms which continued to victimize both the land and its inhabitants. Both nineteenth-century homesteading (based on the Homestead Act of 1862) and agribusiness, its twentieth century descendant (born from the failure of the Homestead Act), relied on the (mis)use of water to accomplish their respective goals. And both policies resulted in ecological disaster.
David N. Cassuto, Turning Wine Into Water: Water as Privileged Signifier in the Grapes of Wrath, 29 Papers on Language and Literature 67 (1993), http://digitalcommons.pace.edu/lawfaculty/458/.