Just to clarify this is not exactly true. It was the original idea, but pretty quickly they realized that it wasn't a practical definition and kilogram ended up being defined by a standard reference object which was carefully stored in a vault in Paris and thus being disconnected from the meter and the density of water. Finally in 2019 kilogram was redefined again in terms of natural constants in the great SI unit upheaval. Although sadly the new definition is not very intuitive to understand.