Collection of liquid into containers

The ability to collect liquid into containers.
How this is represented as entities needs to be thought out though.
Either the liquid is represented by an attribute on the container, such as "liquid=water", and the amount by another attribute on the container, such as "contents=1" for i litre.
Or the water is a separate entity, which is a child of the container. This would perhaps better fit with how the rest of the world is set up, but will require some extra logic whenever the liquid is transferred. In this second scheme, one would think that the container would have an attribute specifying its volume, and then the contained liquid would also have a volume attribute. If one tried to put a liquid with to large a volume into a smaller container, the surplus would spill over (creating a new liquid entity which would then move on, soaking stuff and then ending up in another container or the ground).