The network of icons in the simulator window consists of both water handling objects (reservoirs, confluences, diversions) and tables. Naturally, it is the water handling objects that are the reason for the entire model in that they model corresponding structures in the basin.

The water handling objects have a fixed collection of slots the first two of which are always inflow and outflow. What happens within the icon, i.e., between the inflow and the outflow slots, represents the essence of the differences among the water handling objects. It is inside the object that consumptive use, losses, power generation, etc. takes place. These processes are controlled by the laws of physics and by the parameters and policies that the modeler loads through the GUI.

Water handling objects are connected by directional links which represent the flow of water from the outflow slot of the upstream node to the inflow slot of the downstream node. Note that while table slots may freely be linked to other slots in the system, there is no such freedom between water handlers. The linking is always from outflow to inflow and is performed automatically by the system once the user has indicated which two nodes to connect.

Water handling objects are controllable. They are able to respond to policies that the modeler wishes to simulate. To control the behavior of a water object, the modeler can control release and storage (on reservoirs). These controls will be obeyed so long as they do not violate the laws of physics. For example, a requested release from a reservoir will only be made if there is enough water either in that reservoir or in reservoirs upstream.

In the event that there are conflicting policies specified, RiverSim has a weighting scheme that may be used to balance goals. See the Policy section for a more complete discussion.