The first time he said that, I replied with, "What are you going to change it into?" Of course I didn't get a reply. So later I asked him in all seriousness, what he meant.
So now, as I understand it, it's what he has to do when he "flood irrigates" a field. He builds a dam in the irrigation ditch, so that the water overflows into the field and floods it. Every so often you have to go and take the dam out of one part of the ditch and put it in another part of the ditch so that it can flood another part of the field.
So that is what he means when he says, "I've got to go change water." He really could say, "I've got to go and move the dam." Same thing. But I guess the latter is not farmer talk.
Since I'd been asking so many questions, he invited us to go with him one night when he had to change water. Here's what it looks like. The dams are pretty high-tech.
He uses some sticks and a tarp.....and some really cool rubber boots
Puts the sticks in the ditch
Sets up the tarp against the sticks
And by then I was wishing I had some cool rubber boots too. My feet were soaked!
So there you have it folks. That is how you "change water."