I think this is fascinating, and disturbing (from the essay "Torture and Religious Practice" by William Schweiker, a religion professor at the University of Chicago):
"Why the use of water? Consider a tiny fragment of a complex history. In the case of the Anabaptists, the answer to the question about water is simple and clear. Roman Catholics and Protestants alike persecuted the Anabaptists, or "re-baptizers," since these people rejected infant baptism in favor of adult baptism...
Water as a form of torture is an inversion of the waters of baptism under the (grotesque) belief that it can deliver the heretic from his or her sins. It was believed — at least since St. Augustine — that punishment, even lethal in form, could be an act of mercy meant to keep a sinner from continuing in sin, either by repentance of heresy or by death... Interestingly, beliefs about divine mercy and the ultimate good of salvation were the fuel driving polices that justified the use of torture.
In the Inquisition, the practice was not drowning as such, but the threat of drowning, and, symbolically we can say, the threat of baptism. The tortura del agua or toca entailed, like waterboarding, forcing the victim to ingest water poured into a cloth stuffed into the mouth in order to give the sense of drowning. Because of the broad symbolic meaning of 'water' in the Christian and Jewish traditions (e.g., creation, the great flood, the parting of the Red Sea in the Exodus and drowning of the Egyptians, Christ's walking on the water, and, centrally for Christians, baptism as a symbolic death that gives life, as in St. Paul's theology of baptism in Romans 6), the practice takes on profound religious meanings.
Torture has many forms and meanings, of course, but torture by water as it arose in the Roman Catholic and Protestant Reformations drew some of its power and inspiration from theological convictions about repentance and salvation. It was, we must surely say, a horrific inversion of the best spirit of Christian faith and symbolism.
This poses questions. Is it the purpose of the United States nowadays to seek the conversion, repentance, and purity of supposed terrorists and thus give waterboarding on the trappings of a religious rite? Is waterboarding a kind of forced conversion hidden within a political action and thereby all the more powerful as a tool in the hands of the state to demonize its enemy? Does this signal a breakthrough of the demonic within political and military action since a religious rite is being subverted for immoral ends? These questions are so buried in public discourse that their full import is hardly recognized, even by devout Christians."