14+ feet would be BEST, but over the years my team of experts
Dennis, Jerry and Mike have been able to develop pretty good wakes in water depths of a maximum of 8 feet. We hosted contests for the folks at the NorCal INT League several times up at Villa Lagos, a man-made wakeboarding lake. It's maximum depth, as I said, is 8 feet and I'd guess shallower than that, more often than not.
The key seems to be more about "sinking" the entire boat, rather than just focusing on the one rear corner. A more even distribution of the weight gave better results.
Like Matt points out, not ideal, but doable.
This is a link to last years contest so you can see some of the pictures:
http://www.wakeworld.com/MB/Discus/messages/87668/355203.html One picture so you don't have to slog through that thread.