http://green.blogs.nytimes.com/2011/03/21/divvying-up-the-water-down-under/

In Australia, each right to use water within a specific basin is
awarded as a percentage of all available water in a given year. Priority is
given to permanent crops like nut trees or grapevines, although even these can
run short of water when severe drought hits. Water-intensive annual crops like
rice and cotton are the first to be abandoned in dry years.

But in California, rights to use specific amounts of water are assigned on a
priority basis in a system analogous to mining claims. Whoever put that water to
use first gets to keep all of the allocation until it runs out. The rights
remain theirs no matter what they are farming, even if their crops might be
judged second-, third- or, most likely, fourth- or fifth-priority.

The ownership system of water in Australia was transformed so that allocations
of water no longer are no longer directly tied to the land being farmed: the
rights are a separate property that can be sold, traded or leased.

During the drought, Mr. Gregson said, “water efficiency increased dramatically.”
He added, “If we put a dollar value on every liter of water a farmer uses they
will necessarily use it to its most efficient level.”