TL;DR at the end.

The only similar example I could think of is truck drivers who ship gasoline in a tanker trucks. For them, it costs about $1000 for every 100 miles. The only place I can find in the USA right now that has crops to grow food and that is also having a drought is Kansas. Let’s pretend they are having flooding in Houston (which happened a few years ago). Houston Texas to Garden City Kansas is a 768 mile drive. So that one shipment would cost $7680.

The smallest tanker truck only holds 3000 gallons but the largest holds over 11,000. So let’s assume you are using the larger one.

It takes 325,000 gallons of water in a growing season for an acre of corn. The average size of a corn farm is 333 acres. That means that the average farm would need 108 million gallons of water just for that farm. 108 million divided by 11,000 gallons in the tanker truck is about 10,000 trips from Houston to Garden City. 10,000 trips times $7680 per trip is $76,800,000.

So, for a single farm to ship all the water it needs for a growing season from the nearest flood would be 76.8 million dollars. This is for a normal growing season without a drought so in reality, you would probably need more water than that but I don’t know how to figure that out. These costs are for shipping only and you would have other costs to include all the labor and infrastructure to make all this happen. Also, the USA only has 100,000 tanker trucks of any size and we’ve only been talking about a single farm.

There are 60,000 farms in Kansas so the cost to ship water to all the farms in that state would be $46 trillion for a growing season.

TL;DR: $76.8 million for one Kansas farm and $46 trillion for all the farms in Kansas which only includes shipping costs (assuming we had enough trucks and drivers which we don’t).

Source: lots of googling and tons of quarantine boredom.