Any sanitary district created hereunder, after being authorized by an affirmative vote of the legal voters of the district at an election to be held as is hereinafter provided, may acquire, purchase or construct waterworks, and thereafter operate, improve and extend such waterworks as defined herein, and pay the cost of such purchase, construction, improvement or extension by the issuance and sale of general obligation bonds, revenue bonds or special assessment bonds of the district, which revenue bonds shall be payable solely from the revenue to be derived from the operation of the waterworks.