It was put in by the same guys who are doing the grading/driveway work. Should I ask them to dig it down two feet and case it in another pipe? I'm not sure that I want that pipe cased in concrete.
All soil moves. Some soil moves more then other soil. Pipes in the ground break because they cannot handle all the movement of the soil.
Putting the water line inside another pipe allows the water line pipe to move, which reduces that chance of failure. Pouring concrete onto the water line would increase it's likelihood of failure because the concrete will move with the soil and stress the pipe.
If for some reason the water line ever failed, you could replace it because it is inside another pipe.
The only other option that might work is to bury the pipe at the bottom of the ditch going through the creek with a layer of sand, then pouring the concrete on top of the sand. I know that some cities do something similar to this.
When burying a line under a creek, the few times I've seen it done, they dig the trench and use the dirt to dam up the creek. You can only do this when it's flowing slowly, or not at all. Then after the trench is dug, they lay the pipe with the sleeve in the trench and then back up the cement truck and dump a couple of yards of concrete into the trench. I have never seen them take down the temporary dam. I was told it will wash away on it's own and it's better to let the concrete set without the water over it as long as possible.
This is here in my area of Texas.
I would either try to look up what code is there, or go talk to somebody at the Water Utility to see how they do it. I would consider what the Water Utility does to be gospel and I would do it exactly how they say to do it. I would not pay your plumber until it's done correctly. He might charge you more, but whatever it takes, I would not leave it like that.