Moving large quantities of water long distances is expensive. But there are alternatives:

The third-generation dairy farmer was forced to idle a quarter of his 1,200 acres in Tulare County, land that once also bristled with wheat and alfalfa. Now he is buying feed from out of state, paying record-high prices to contractors in Nevada, Texas and as far as Australia for alfalfa hay and corn silage.

Moving the water itself from Australia to California would be prohibitively expensive, you understand. But the alfalfa, apparently less so.