Indiana Code Title 36. Local Government § 36-10-4-37

Sec. 37. (a) All proceeds from the sale of bonds issued under section 35 of this chapter shall be kept as a separate fund to pay for:

(b) The fund may not be used for any other purpose.  The fund shall be deposited, at interest, with the depository or depositories of other public funds of the city, and all interest collected on it belongs to the fund.  A surplus remaining from the proceeds of the bonds after all costs and expenses are fully paid shall be paid into and becomes a part of the district bond fund.