Water accounting policy expression is different from simulation policy expression, although some of the tools are identical. Simulation policy determines where the physical water moves and is stored; accounting policy determines who owns the water but does not cause any water to be moved. Water policy is implemented at the end of each time step in the simulaition meta algorithm and adjusts credits based on the results of the simulation time step.

There are four tools for setting accounting policy:

• The demand delivery dialog which allows the setting of delivery amounts and locations.

• The account bin dialog which allows setting policy with respect to spills.

• The account rule dialog which allows specifying rules for the allocation of systems losses and gains among account bins.

• The bin evaluation order which allows specifying the order in which the bin rules at a node will be evaluated.