The bonded indebtedness of a city of the metropolitan class shall not at any time exceed in the aggregate five percent of the taxable value of the taxable property within its corporate limits. The value shall be determined from the assessment of the taxable value of the property of the city. In order to arrive at the net amount of the aggregate indebtedness referred to in this section, there shall be deducted from the total bonded indebtedness of the city and excepted from such indebtedness bonds issued to acquire a water plant or gas plant and any bonds which may be issued to acquire or construct electric light or power plants or other utility plants or systems when a charge for the service is provided sufficient to pay the bonded obligations for such plants or systems, bonds which may be issued to construct subways or conduits when the revenue charged for the use of such may be sufficient to retire such bonds, and all other bonds the payment of which is secured by pledges of a special assessment sinking fund in the nature of a sinking fund of any character other than the general sinking fund of the city. There shall be included in such indebtedness all floating indebtedness of the city which under section 14-524 may be funded by the issuance of bonds.