Do you know who would do that? Torchwood Team Cardiff.
Gwen would be all, “We shouldn’t do this!” But Jack would be firm about it, and she wouldn’t argue too strenuously. He would probably hold the victim under the water himself—Jack generally doesn’t expect his team to do the dirty work. And Ianto might make inappropriate jokes, if this happened at around the same time as Sleeper. And Owen and Tosh would look upset, but they would go along with it. Tosh would cover it up afterwards, hide the body, and go back to worrying about her love life. And if the person drowned, they would all be sad about it for awhile, but the needs of the many outweigh the needs of the one, etc., and they would eventually get distracted by other things. Except Gwen might be so traumatized about it that she would have sex with Owen, depending on when this takes place. And then of course everyone gets so caught up in the fact that she’s having sex with Owen that they forget about the poor, dead, innocent person. And it's back to business-as-usual.