A district with revenues from the operation of facilities, improvements or projects of the district may issue bonds without the necessity of holding an election and as an alternative or in addition to other forms of borrowing authorized in this chapter, for the purpose of acquiring or improving the facilities, improvements or projects and such bonds must be made payable solely out of the net revenues derived from the operation of such facilities, improvements or projects. A single bond issue may be had for more than one of such facilities, improvements or projects and the revenues for any and all of the income-producing facilities, improvements and projects may be pledged to pay for any other such facilities, improvements or projects. To that end, a single fund may be established and maintained.