It looks like Dumbledore had the ability to kill Voldemort in Harry Potter And The Order of the Phoenix (when he encased Voldemort's body in a bubble of water) but chose not to do so;
Dumbledore brandished his wand in one long, fluid movement – the snake, which had been an instant from sinking its fangs into him, flew high into the air and vanished in a wisp of dark smoke; and the water in the pool rose up and covered Voldemort like a cocoon of molten glass.
For a few seconds Voldemort was visible only as a dark, rippling, faceless figure, shimmering and indistinct upon the plinth, clearly struggling to throw off the suffocating mass –
Then he was gone and the water fell with a crash back into its pool, slopping wildly over the sides, drenching the polished floor.
My question is; what would happen if Dumbledore (or someone else) had actually tried to kill Voldemort? If Voldemort had many other Horcruxes, would he have drowned in Dumbledore's bubble of water, for example?