It is a common assumption , stated as part of these puzzles , that the jugs in the puzzle are irregularly shaped and unmarked .
It is impossible to accurately measure any quantity of water that does not completely fill a jug .
It is a common assumption , stated as part of these puzzles , that the jugs in the puzzle are irregularly shaped and unmarked , so that it is impossible to accurately measure any quantity of water that does not completely fill a jug .