Actually , regulating water ...

Actually , regulating water for preventing export of corn for biofuel is not possible. It can be challenged and very easily can be won by the farmers because you are not regulating corn production and its usage but you are regulating water uses for irrigation. Once you regulate the irrigation water uses it would be applicable for producing all kinds of crop. There would be no discrimination between uses. Farmers are free to chose which products they have to produce for their livelihood. The product must not fall in the category of restricted weeds or product etc. No on can prevent them to use water for irrigation. Instead one can suggest law maker to limit the export or application of corn for up to 50 % for its industrial application so that farmers get benefited by selling for both tortillas as well as biofuels.