I have to agree with you here. I would feel more comfortable using a 2x4 and level too. The way I did mine though is I borrowed a rotating laser level from work and used it to get it right.

But a water leve is pretty basic. you need a clear tube, and you would pound a stake in someplace and tie the tube to the stake, fill it with water (probably with a garden hose I would imagine). Then you should probably hold the ends together and measure down to wherever you want the finished grade to be. What ever it is, you would have to walk around and just measure down, say if it is 12 inches at the stake, then no matter what it would always be 12 inches down from the water level, so you would just check it as you walk around.

My whole problem with it is that if you set the tube down, it is obviously going to drain out, so someone would have to do that for you, which would mean that someone would be doing all of the work and someone would be the bearer of bad news.

I always see the water level pushed on here, but in this day and age, there are WAY better solutions, rotating laser levels are pretty commonplace now, although the one I used had a transciever that beeps at you when you are dead on. The cheap ones you actually have to see the beem, I am sure you can rent them though.

Site Levels are also good just for getting the perimeter level. The kind you set on a tripod and look through. When I did mine, I predug everything to within about 1.5 inches tolerance, then I set all my blocks dead on, and made things work from there, you could sweep a 2x4 from each block in an arc and have a center benchmark too.

Get this right, once the water is in it, you will see whether or not it is good. And if you are like me, it will bother you if it is not.

steve