Firstly, the water mostly doesn't leave california. If they're exporting dried rice and almonds and things like that, most of the irrigation water is staying right where it was used, correct? You say water is consumed, as if it goes away or vanishes? Evaporated water or underground water is also water.

Secondly, you're giving jobs and supporting the local economy. Farmers purchase supplies, capital goods, they pay property taxes, and first and foremost they employ people. They employ large workforces. All that revenue they received from selling wherever they sell is stimulating local economies.

Lastly, exporting food is great international relations. What country will attack you when they depend on you for food? What nation will not be grateful for receiving such basic sustenance from overseas? And if we would go to war, and if you want to shut down all this agriculture, what will we eat on the home front? If we can't import food, we'd better have infrastructure to support our own needs. Any nation [state, county, city] that produces excess food is more likely to withstand siege, blockade or attack.

Liquor and soda bottlers can pivot to producing and distributing hand sanitizer or bottled water. If beer or Coke is bad for you, keep drinking it anyway, because you never know when that industry will become indispensable.