The solution to this problem is very, very simple: actually force farmers to pay market price for the water they use. The end.
Food stamps are a far far better way of subsidizing food for the poor than through a rube goldberg system of supposedly helping the poor by giving millions to huge agribusinesses. So much so that I consider those types of arguments a bit of a red herring. Along with the "food security" argument -- there's no impeding worldwide embargo of the united states and if there were calories would be the least of our problems.
I would assume that instead of keeping food prices down, farming subsidies will drive farming land prices up.
The US is a big country, there's no need to grow almonds in the desert.