Full Idea
For Chalmers, 'water' is two-dimensionally inconstant, in that it has different secondary intensions relative to different worlds of utterance.
Clarification
The 'intension' is what picks out the instances of water
Gist of Idea
'Water' is two-dimensionally inconstant, with different intensions in different worlds
Source
report of David J.Chalmers (Foundations of Two-Dimensional Semantics [2006]) by Theodore Sider - Four Dimensionalism 7.2
Book Reference
Sider,Theodore: 'Four Dimensionalism' [OUP 2003], p.108
A Reaction
In this way 'water' is regarded as being like an indexical (such as 'I'), which has a fixed meaning component, and a second component which varies with different utterances. Maybe.