85-1-321. Funds in general. The department shall create a fund to be known as the "administration fund" and shall also create three separate funds in respect of the bonds of each series, one fund to be known as the "construction fund, series....", another fund to be known as the "water fund, series....", and another fund to be known as the "debt service fund, series....", each fund to be identified by the same series letter or letters as the bonds of the series. The money in each fund must be deposited in a depository or depositories and secured in the manner determined by the department. It is lawful for any bank or trust company incorporated under the laws of this state to act as the depository and to furnish indemnifying bonds or to pledge securities as may be required by the department. A separate account must be kept in each construction fund and in each water fund for each project. All expenditures not properly chargeable to the construction fund account or to the water fund account of any one project must be charged by the department in proportions as it shall determine to the construction fund accounts or to the water fund accounts, as the case may be, of the projects in respect of which the expenditures were incurred.