A city, in order to protect the public health, may adopt an ordinance to provide for the separation of storm water drainage and footing drains from sanitary sewers on privately owned property. The legislative body of a city may determine that the sewer separation authorized by this section is for a public purpose and is a public improvement and may also determine that the whole or any part of the expense of these public improvements may be defrayed by special assessment upon lands benefited by the public improvement or by any other lawful charge. A special assessment authorized by this section shall be considered to benefit only lands where the separation of storm water drainage and footing drains from sanitary sewers occurs.