The metric system has nothing to do with being defined by either the weight or volume of a bucket of water. It is based on the METRE. The original definition of the metre was 10000KM was the distance from the north pole to the equator. From that 1CM cubed gives you a Millilitre. 1000Millilitre = Litre. 1 litre water weighs 1KG. And so on.
All of them, only yanks call them duck-billed