I was reading about this just the other day!
Here`s what my book says:
This is a behaviour that is based on the ancient lifestyle of the cat family. Wild cats bring dead prey back to their lair or nest; hunting domestic cats often come home with a dead mouse or frog. The nest, the home - these are the safe, secure points of their territory. A domestic cat that does not or cannot go out hunting still has the powerful feline hunting urge which it displays when it stalks, chases after and pounces on toys, pieces of paper or balls of wool in play. In the home, particularly in a multi-cat household, it may not have one particular nest, so it instinctively takes it`s 'prey' to the place that is at the centre of its daily life - the food or water bowl - and deposits it there.