Revenues and moneys raised by taxation in special districts of the city shall be divided into the following special funds:

   First, A street district fund, for each street district,—for defraying the expenses of grading, improving, repairing and working upon the streets therein, and for the payment of all street expenses, which the council shall charge upon the street district;

   Second, A district sewer fund, for each main sewer district,—for the payment of the costs and expenses of sewers and drainage in, and chargeable to the main sewer district, when the city shall be divided into such districts;

   Third, Special assessment funds; any money raised by special assessment levied in any special assessment district or special sewer district to defray the expenses of any work, paving, improvement, repairs, or drainage therein, shall constitute a special fund for the purpose for which it was raised.