In some parts of the world water is literally free, you only have to pay for the connection. Whereas in others there's a shortage and people have to resort to clever engineering, like Israel with desalination or Libya with the Great Man-Made River project. In both of those cases the problem would be trivial if global transportation costs were zero.
Even with oil it is a thing - there's a different spot price and different forward curve at each tradeable terminal. For example the recently famous negative prices (and the monster contango) were observed only in Cushing, OK; other ports were always > 0. With water the difference would be much larger.