A.R.S. § 48-631

Municipal corporations may incur a bonded indebtedness to provide a fund to be called a "general improvement fund." The fund may be invested or reinvested in any bonds issued for work and public improvements, the cost of which in whole or in part is to be ultimately paid by assessments levied against lots or land benefited thereby, or issued to pay the cost of land purchased or condemned for such work or public improvements. The bonds shall be called "investment bonds."