Tantalus is a character from Greek mythology who did some bad things (trying to feed his son to the gods), and in turn was punished in Tartarus:
Tantalus (Ancient Greek: Τάνταλος, Tántalos) was a Greek mythological figure, most famous for his eternal punishment in Tartarus. He was made to stand in a pool of water beneath a fruit tree with low branches, with the fruit ever eluding his grasp, and the water always receding before he could take a drink.
The Greeks weren't too concerned with making the mechanics of this torture, because they had the god's magic powers to help them out.
A warden in the near-future (year 2,400) who has an ironic adoration of Greek mythology comes up with the scheme to punish prisoners who misbehave in a similar situation.
Our warden fellow needs to have 'water' that forms a depression when the prisoner bends down from his bindings to drink.
How could the warden create this effect with water?
Money is not an issue. The government spares no expense when it comes to making these prisoners have a hard time.