A couple fortresses ago, I decided to move water from the source of a brook right outside to a very large indoor cistern. I was really pleased with the setup I had.
On the top Z-level, I had a well. I went ahead and built it even before the cistern had gotten any water in it, because hey, why not?
On the level right below the well, I had an access platform and a wide pit. Dwarves go here to fill up the well with their buckets. (I had designated every square of the pit as a separate pond, in order to let the dwarves do more than one "Fill Pond" job at a time.)
Eight or nine levels below the pit/pond level were the actual cistern level. I had mined out about a 7x7 space on each one (with supports to avoid collapses.) This was a huge cistern, and would hold a lot of water, but would take a long, long time to fill.
Anyway, I let my dwarven bucket brigade go to work, checking back on them every once in awhile to make sure it's still making progress. Before long, they had enough water in the bottom Z-level that the well no longer counted as "dry." Good!
Then I noticed that progress seemed to stop. After a little investigation, it turned out that the dwarves had stopped using the brook as a water source to fill the cistern, and had started using the well instead. They were using the well to pull up water from the cistern, then running down a flight of stairs and dumping water back in the same cistern.