I figured out through trial and error how to make springs in an arbitrary body of water. Basically, you have to place water in a checkerboard pattern. If you don't know how to make an infinite spring, it's easy. Gather up 2 buckets of water, dig a 2x2x1 hole, then dump one bucket into one corner, and the other bucket in the diagonally-opposite corner. Voila! You can pick up water from this hole as many times as you want and it will never go away. And when you want to get rid of it, just fill with dirt (or whatever) and it's gone. I usually do that then get 9 buckets of water to go around leveling things off. I had to do that for the moat around my castle.