A 'Water in Jugs' has a weight of 2 and a bulk of 1 (an empty jug has weight 1, bulk 1).
NOTE: When donating water in jugs to a construction site or to a University, you must be holding one more than you are donating. Presumably, this restriction is to prevent people from carelessly using up their last jug, rendering themselves unable to gather clay and make more jugs.