You could safely do away with most of the Clean Water Act verbiage by simply requiring all inlets to be downstream of its associated discharge. The owner of the facility in question would find it much easier to clean up the discharge than strain out the garbage at the inlet.
Water supply and wastewater treatment facilities are not always under the same operating authority. Furthermore, it neglects towns whose water source may come from wells, and runoff pollution from other sources. Then you have the existance of natural, local monopolies over water distribution. There would be no competitive pressure for the private supplier to improve water quality.
Frankly, privatization of water supply and treatment facilities is an absurd proposition.