That must have been a bit of a trick out in the middle of the desert!
Where did all that water originate?
Maybe denial isn't a river in Egypt, but Da Nile is. 
Really, they had to have had water for the workers to drink anyway, so
they likely had enough extra around to set up a few bowl or trough levels.
4000 years ago it was a lush green agricultural paradise. Today's desert
(in the valleys of the pyramids at least) is some combination of natural
events and poor farming, grazing and forest practices ...