To track the paper water that is moving through the system, accounts are created on the simulation objects. An account is an object used to track the inflow, outflow, and storage of paper water on the simulation object. Like simulation objects, given the required knowns, the accounts can solve for certain unknowns.

Accounts can be defined as either legal accounts or passthrough accounts. The types of allowable accounts depend on the type of simulation object on which the account resides.

Accounts have user-selectable methods that control how the accounts behave. For example, the user can select a carryover method where all of the storage in the account carries over from one water year to the next. Alternatively, the user can configure the account such that the storage in the account is reset at the beginning of the water year. Provided for each account in Account Reference is a description of each category and the methods in that category including the method-specific slots.

Accounts solve when they have the required information. Unlike simulation, accounts typically solve in the downstream direction. Storage accounts usually solve for Storage and passthrough accounts usually solve for Outflow, but never for Inflow. Each type of account is described in more detail in the Account Reference including the solution equations for each type of account. See How the Accounting System Solves for additional information on how the accounting system solves.

In addition to the slots that reside on each account, there are variables that can be used to describe the account including Water Type and Water Owner. These properties are used to keep accounts clearly identified and, as we will see later, used by predefined functions to access the correct account.

Water Type is a property of an account that can be used to describe that account. Typically, Water Type is used to classify where the water originated or where it is going. For example, in a model with a trans-basin diversion, the user could define two water types, Type A and Type B, one for each basin. When water is diverted trans-basin, the Water Type can be used to track water from basin A when it is in basin B. The default Water Type is NONE.

Water Owner is another property of accounts used to classify or describe an account. Typically, the Water Owner is used when a volume of water is owned by a specific user who wants to track that water through a basin. For example, a city might own a set volume of water in an upstream reservoir. The default Water Owner is NONE.

By defining both Water Type and Water Owner, the user can track the classification of a wide range of water. If we combine the two examples above, the city might own some of the trans-basin water but cannot use it until it is diverted from Basin A to Basin B and flows downstream to the city. By defining both Water Type and Water Owner, the city can track that the water released for the city (which is located in Basin B) is from Basin A and owned by the city.

The Water Owner and Water Type are defined in the Accounting System Configuration and apply to a specific model. When configuring an individual account, the default Water Owner and Water Type is NONE but can be changed by the user.

Legal accounts (Storage, Diversion, Instream Flow) can have a priority date associated with the account. Specified in the account’s configuration window, the priority date is a fully specified date and time. If the Water Rights method is selected on the account, then a Priority Date must be specified and vice versa. The Priority Date is used by the water rights allocation solver to allocate flow to the account. See Water Rights Allocation for details.